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<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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<!-- File: $Id: Bv9ARM-book.xml,v 1.478.8.20 2011-11-09 05:53:35 each Exp $ -->
<book xmlns:xi="http://www.w3.org/2001/XInclude">
<title>BIND 9 Administrator Reference Manual</title>
<bookinfo>
<copyright>
<year>2004</year>
<year>2005</year>
<year>2006</year>
<year>2007</year>
<year>2008</year>
<year>2009</year>
<year>2010</year>
<year>2011</year>
<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
</copyright>
<copyright>
<year>2000</year>
<year>2001</year>
<year>2002</year>
<year>2003</year>
<holder>Internet Software Consortium.</holder>
</copyright>
</bookinfo>
<chapter id="Bv9ARM.ch01">
<title>Introduction</title>
<para>
The Internet Domain Name System (<acronym>DNS</acronym>)
consists of the syntax
to specify the names of entities in the Internet in a hierarchical
manner, the rules used for delegating authority over names, and the
system implementation that actually maps names to Internet
addresses. <acronym>DNS</acronym> data is maintained in a
group of distributed
hierarchical databases.
</para>
<sect1>
<title>Scope of Document</title>
<para>
The Berkeley Internet Name Domain
(<acronym>BIND</acronym>) implements a
domain name server for a number of operating systems. This
document provides basic information about the installation and
care of the Internet Systems Consortium (<acronym>ISC</acronym>)
<acronym>BIND</acronym> version 9 software package for
system administrators.
</para>
<para>
This version of the manual corresponds to BIND version 9.8.
</para>
</sect1>
<sect1>
<title>Organization of This Document</title>
<para>
In this document, <emphasis>Chapter 1</emphasis> introduces
the basic <acronym>DNS</acronym> and <acronym>BIND</acronym> concepts. <emphasis>Chapter 2</emphasis>
describes resource requirements for running <acronym>BIND</acronym> in various
environments. Information in <emphasis>Chapter 3</emphasis> is
<emphasis>task-oriented</emphasis> in its presentation and is
organized functionally, to aid in the process of installing the
<acronym>BIND</acronym> 9 software. The task-oriented
section is followed by
<emphasis>Chapter 4</emphasis>, which contains more advanced
concepts that the system administrator may need for implementing
certain options. <emphasis>Chapter 5</emphasis>
describes the <acronym>BIND</acronym> 9 lightweight
resolver. The contents of <emphasis>Chapter 6</emphasis> are
organized as in a reference manual to aid in the ongoing
maintenance of the software. <emphasis>Chapter 7</emphasis> addresses
security considerations, and
<emphasis>Chapter 8</emphasis> contains troubleshooting help. The
main body of the document is followed by several
<emphasis>appendices</emphasis> which contain useful reference
information, such as a <emphasis>bibliography</emphasis> and
historic information related to <acronym>BIND</acronym>
and the Domain Name
System.
</para>
</sect1>
<sect1>
<title>Conventions Used in This Document</title>
<para>
In this document, we use the following general typographic
conventions:
</para>
<informaltable>
<tgroup cols="2">
<colspec colname="1" colnum="1" colwidth="3.000in"/>
<colspec colname="2" colnum="2" colwidth="2.625in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>To describe:</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>We use the style:</emphasis>
</para>
</entry>
</row>
<row>
<entry colname="1">
<para>
a pathname, filename, URL, hostname,
mailing list name, or new term or concept
</para>
</entry>
<entry colname="2">
<para>
<filename>Fixed width</filename>
</para>
</entry>
</row>
<row>
<entry colname="1">
<para>
literal user
input
</para>
</entry>
<entry colname="2">
<para>
<userinput>Fixed Width Bold</userinput>
</para>
</entry>
</row>
<row>
<entry colname="1">
<para>
program output
</para>
</entry>
<entry colname="2">
<para>
<computeroutput>Fixed Width</computeroutput>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The following conventions are used in descriptions of the
<acronym>BIND</acronym> configuration file:<informaltable colsep="0" frame="all" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="3.000in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="2.625in"/>
<tbody>
<row rowsep="0">
<entry colname="1" colsep="1" rowsep="1">
<para>
<emphasis>To describe:</emphasis>
</para>
</entry>
<entry colname="2" rowsep="1">
<para>
<emphasis>We use the style:</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1" colsep="1" rowsep="1">
<para>
keywords
</para>
</entry>
<entry colname="2" rowsep="1">
<para>
<literal>Fixed Width</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1" colsep="1" rowsep="1">
<para>
variables
</para>
</entry>
<entry colname="2" rowsep="1">
<para>
<varname>Fixed Width</varname>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1" colsep="1">
<para>
Optional input
</para>
</entry>
<entry colname="2">
<para>
<optional>Text is enclosed in square brackets</optional>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect1>
<sect1>
<title>The Domain Name System (<acronym>DNS</acronym>)</title>
<para>
The purpose of this document is to explain the installation
and upkeep of the <acronym>BIND</acronym> (Berkeley Internet
Name Domain) software package, and we
begin by reviewing the fundamentals of the Domain Name System
(<acronym>DNS</acronym>) as they relate to <acronym>BIND</acronym>.
</para>
<sect2>
<title>DNS Fundamentals</title>
<para>
The Domain Name System (DNS) is a hierarchical, distributed
database. It stores information for mapping Internet host names to
IP
addresses and vice versa, mail routing information, and other data
used by Internet applications.
</para>
<para>
Clients look up information in the DNS by calling a
<emphasis>resolver</emphasis> library, which sends queries to one or
more <emphasis>name servers</emphasis> and interprets the responses.
The <acronym>BIND</acronym> 9 software distribution
contains a
name server, <command>named</command>, and a resolver
library, <command>liblwres</command>. The older
<command>libbind</command> resolver library is also available
from ISC as a separate download.
</para>
</sect2><sect2>
<title>Domains and Domain Names</title>
<para>
The data stored in the DNS is identified by <emphasis>domain names</emphasis> that are organized as a tree according to
organizational or administrative boundaries. Each node of the tree,
called a <emphasis>domain</emphasis>, is given a label. The domain
name of the
node is the concatenation of all the labels on the path from the
node to the <emphasis>root</emphasis> node. This is represented
in written form as a string of labels listed from right to left and
separated by dots. A label need only be unique within its parent
domain.
</para>
<para>
For example, a domain name for a host at the
company <emphasis>Example, Inc.</emphasis> could be
<literal>ourhost.example.com</literal>,
where <literal>com</literal> is the
top level domain to which
<literal>ourhost.example.com</literal> belongs,
<literal>example</literal> is
a subdomain of <literal>com</literal>, and
<literal>ourhost</literal> is the
name of the host.
</para>
<para>
For administrative purposes, the name space is partitioned into
areas called <emphasis>zones</emphasis>, each starting at a node and
extending down to the leaf nodes or to nodes where other zones
start.
The data for each zone is stored in a <emphasis>name server</emphasis>, which answers queries about the zone using the
<emphasis>DNS protocol</emphasis>.
</para>
<para>
The data associated with each domain name is stored in the
form of <emphasis>resource records</emphasis> (<acronym>RR</acronym>s).
Some of the supported resource record types are described in
<xref linkend="types_of_resource_records_and_when_to_use_them"/>.
</para>
<para>
For more detailed information about the design of the DNS and
the DNS protocol, please refer to the standards documents listed in
<xref linkend="rfcs"/>.
</para>
</sect2>
<sect2>
<title>Zones</title>
<para>
To properly operate a name server, it is important to understand
the difference between a <emphasis>zone</emphasis>
and a <emphasis>domain</emphasis>.
</para>
<para>
As stated previously, a zone is a point of delegation in
the <acronym>DNS</acronym> tree. A zone consists of
those contiguous parts of the domain
tree for which a name server has complete information and over which
it has authority. It contains all domain names from a certain point
downward in the domain tree except those which are delegated to
other zones. A delegation point is marked by one or more
<emphasis>NS records</emphasis> in the
parent zone, which should be matched by equivalent NS records at
the root of the delegated zone.
</para>
<para>
For instance, consider the <literal>example.com</literal>
domain which includes names
such as <literal>host.aaa.example.com</literal> and
<literal>host.bbb.example.com</literal> even though
the <literal>example.com</literal> zone includes
only delegations for the <literal>aaa.example.com</literal> and
<literal>bbb.example.com</literal> zones. A zone can
map
exactly to a single domain, but could also include only part of a
domain, the rest of which could be delegated to other
name servers. Every name in the <acronym>DNS</acronym>
tree is a
<emphasis>domain</emphasis>, even if it is
<emphasis>terminal</emphasis>, that is, has no
<emphasis>subdomains</emphasis>. Every subdomain is a domain and
every domain except the root is also a subdomain. The terminology is
not intuitive and we suggest that you read RFCs 1033, 1034 and 1035
to
gain a complete understanding of this difficult and subtle
topic.
</para>
<para>
Though <acronym>BIND</acronym> is called a "domain name
server",
it deals primarily in terms of zones. The master and slave
declarations in the <filename>named.conf</filename> file
specify
zones, not domains. When you ask some other site if it is willing to
be a slave server for your <emphasis>domain</emphasis>, you are
actually asking for slave service for some collection of zones.
</para>
</sect2>
<sect2>
<title>Authoritative Name Servers</title>
<para>
Each zone is served by at least
one <emphasis>authoritative name server</emphasis>,
which contains the complete data for the zone.
To make the DNS tolerant of server and network failures,
most zones have two or more authoritative servers, on
different networks.
</para>
<para>
Responses from authoritative servers have the "authoritative
answer" (AA) bit set in the response packets. This makes them
easy to identify when debugging DNS configurations using tools like
<command>dig</command> (<xref linkend="diagnostic_tools"/>).
</para>
<sect3>
<title>The Primary Master</title>
<para>
The authoritative server where the master copy of the zone
data is maintained is called the
<emphasis>primary master</emphasis> server, or simply the
<emphasis>primary</emphasis>. Typically it loads the zone
contents from some local file edited by humans or perhaps
generated mechanically from some other local file which is
edited by humans. This file is called the
<emphasis>zone file</emphasis> or
<emphasis>master file</emphasis>.
</para>
<para>
In some cases, however, the master file may not be edited
by humans at all, but may instead be the result of
<emphasis>dynamic update</emphasis> operations.
</para>
</sect3>
<sect3>
<title>Slave Servers</title>
<para>
The other authoritative servers, the <emphasis>slave</emphasis>
servers (also known as <emphasis>secondary</emphasis> servers)
load
the zone contents from another server using a replication process
known as a <emphasis>zone transfer</emphasis>. Typically the data
are
transferred directly from the primary master, but it is also
possible
to transfer it from another slave. In other words, a slave server
may itself act as a master to a subordinate slave server.
</para>
</sect3>
<sect3>
<title>Stealth Servers</title>
<para>
Usually all of the zone's authoritative servers are listed in
NS records in the parent zone. These NS records constitute
a <emphasis>delegation</emphasis> of the zone from the parent.
The authoritative servers are also listed in the zone file itself,
at the <emphasis>top level</emphasis> or <emphasis>apex</emphasis>
of the zone. You can list servers in the zone's top-level NS
records that are not in the parent's NS delegation, but you cannot
list servers in the parent's delegation that are not present at
the zone's top level.
</para>
<para>
A <emphasis>stealth server</emphasis> is a server that is
authoritative for a zone but is not listed in that zone's NS
records. Stealth servers can be used for keeping a local copy of
a
zone to speed up access to the zone's records or to make sure that
the
zone is available even if all the "official" servers for the zone
are
inaccessible.
</para>
<para>
A configuration where the primary master server itself is a
stealth server is often referred to as a "hidden primary"
configuration. One use for this configuration is when the primary
master
is behind a firewall and therefore unable to communicate directly
with the outside world.
</para>
</sect3>
</sect2>
<sect2>
<title>Caching Name Servers</title>
<!--
- Terminology here is inconsistent. Probably ought to
- convert to using "recursive name server" everywhere
- with just a note about "caching" terminology.
-->
<para>
The resolver libraries provided by most operating systems are
<emphasis>stub resolvers</emphasis>, meaning that they are not
capable of
performing the full DNS resolution process by themselves by talking
directly to the authoritative servers. Instead, they rely on a
local
name server to perform the resolution on their behalf. Such a
server
is called a <emphasis>recursive</emphasis> name server; it performs
<emphasis>recursive lookups</emphasis> for local clients.
</para>
<para>
To improve performance, recursive servers cache the results of
the lookups they perform. Since the processes of recursion and
caching are intimately connected, the terms
<emphasis>recursive server</emphasis> and
<emphasis>caching server</emphasis> are often used synonymously.
</para>
<para>
The length of time for which a record may be retained in
the cache of a caching name server is controlled by the
Time To Live (TTL) field associated with each resource record.
</para>
<sect3>
<title>Forwarding</title>
<para>
Even a caching name server does not necessarily perform
the complete recursive lookup itself. Instead, it can
<emphasis>forward</emphasis> some or all of the queries
that it cannot satisfy from its cache to another caching name
server,
commonly referred to as a <emphasis>forwarder</emphasis>.
</para>
<para>
There may be one or more forwarders,
and they are queried in turn until the list is exhausted or an
answer
is found. Forwarders are typically used when you do not
wish all the servers at a given site to interact directly with the
rest of
the Internet servers. A typical scenario would involve a number
of internal <acronym>DNS</acronym> servers and an
Internet firewall. Servers unable
to pass packets through the firewall would forward to the server
that can do it, and that server would query the Internet <acronym>DNS</acronym> servers
on the internal server's behalf.
</para>
</sect3>
</sect2>
<sect2>
<title>Name Servers in Multiple Roles</title>
<para>
The <acronym>BIND</acronym> name server can
simultaneously act as
a master for some zones, a slave for other zones, and as a caching
(recursive) server for a set of local clients.
</para>
<para>
However, since the functions of authoritative name service
and caching/recursive name service are logically separate, it is
often advantageous to run them on separate server machines.
A server that only provides authoritative name service
(an <emphasis>authoritative-only</emphasis> server) can run with
recursion disabled, improving reliability and security.
A server that is not authoritative for any zones and only provides
recursive service to local
clients (a <emphasis>caching-only</emphasis> server)
does not need to be reachable from the Internet at large and can
be placed inside a firewall.
</para>
</sect2>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch02">
<title><acronym>BIND</acronym> Resource Requirements</title>
<sect1>
<title>Hardware requirements</title>
<para>
<acronym>DNS</acronym> hardware requirements have
traditionally been quite modest.
For many installations, servers that have been pensioned off from
active duty have performed admirably as <acronym>DNS</acronym> servers.
</para>
<para>
The DNSSEC features of <acronym>BIND</acronym> 9
may prove to be quite
CPU intensive however, so organizations that make heavy use of these
features may wish to consider larger systems for these applications.
<acronym>BIND</acronym> 9 is fully multithreaded, allowing
full utilization of
multiprocessor systems for installations that need it.
</para>
</sect1>
<sect1>
<title>CPU Requirements</title>
<para>
CPU requirements for <acronym>BIND</acronym> 9 range from
i486-class machines
for serving of static zones without caching, to enterprise-class
machines if you intend to process many dynamic updates and DNSSEC
signed zones, serving many thousands of queries per second.
</para>
</sect1>
<sect1>
<title>Memory Requirements</title>
<para>
The memory of the server has to be large enough to fit the
cache and zones loaded off disk. The <command>max-cache-size</command>
option can be used to limit the amount of memory used by the cache,
at the expense of reducing cache hit rates and causing more <acronym>DNS</acronym>
traffic.
Additionally, if additional section caching
(<xref linkend="acache"/>) is enabled,
the <command>max-acache-size</command> option can be used to
limit the amount
of memory used by the mechanism.
It is still good practice to have enough memory to load
all zone and cache data into memory — unfortunately, the best
way
to determine this for a given installation is to watch the name server
in operation. After a few weeks the server process should reach
a relatively stable size where entries are expiring from the cache as
fast as they are being inserted.
</para>
<!--
- Add something here about leaving overhead for attacks?
- How much overhead? Percentage?
-->
</sect1>
<sect1>
<title>Name Server Intensive Environment Issues</title>
<para>
For name server intensive environments, there are two alternative
configurations that may be used. The first is where clients and
any second-level internal name servers query a main name server, which
has enough memory to build a large cache. This approach minimizes
the bandwidth used by external name lookups. The second alternative
is to set up second-level internal name servers to make queries
independently.
In this configuration, none of the individual machines needs to
have as much memory or CPU power as in the first alternative, but
this has the disadvantage of making many more external queries,
as none of the name servers share their cached data.
</para>
</sect1>
<sect1>
<title>Supported Operating Systems</title>
<para>
ISC <acronym>BIND</acronym> 9 compiles and runs on a large
number
of Unix-like operating systems and on
Microsoft Windows Server 2003 and 2008, and Windows XP and Vista.
For an up-to-date
list of supported systems, see the README file in the top level
directory
of the BIND 9 source distribution.
</para>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch03">
<title>Name Server Configuration</title>
<para>
In this chapter we provide some suggested configurations along
with guidelines for their use. We suggest reasonable values for
certain option settings.
</para>
<sect1 id="sample_configuration">
<title>Sample Configurations</title>
<sect2>
<title>A Caching-only Name Server</title>
<para>
The following sample configuration is appropriate for a caching-only
name server for use by clients internal to a corporation. All
queries
from outside clients are refused using the <command>allow-query</command>
option. Alternatively, the same effect could be achieved using
suitable
firewall rules.
</para>
<programlisting>
// Two corporate subnets we wish to allow queries from.
acl corpnets { 192.168.4.0/24; 192.168.7.0/24; };
options {
// Working directory
directory "/etc/namedb";
allow-query { corpnets; };
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
</programlisting>
</sect2>
<sect2>
<title>An Authoritative-only Name Server</title>
<para>
This sample configuration is for an authoritative-only server
that is the master server for "<filename>example.com</filename>"
and a slave for the subdomain "<filename>eng.example.com</filename>".
</para>
<programlisting>
options {
// Working directory
directory "/etc/namedb";
// Do not allow access to cache
allow-query-cache { none; };
// This is the default
allow-query { any; };
// Do not provide recursive service
recursion no;
};
// Provide a reverse mapping for the loopback
// address 127.0.0.1
zone "0.0.127.in-addr.arpa" {
type master;
file "localhost.rev";
notify no;
};
// We are the master server for example.com
zone "example.com" {
type master;
file "example.com.db";
// IP addresses of slave servers allowed to
// transfer example.com
allow-transfer {
192.168.4.14;
192.168.5.53;
};
};
// We are a slave server for eng.example.com
zone "eng.example.com" {
type slave;
file "eng.example.com.bk";
// IP address of eng.example.com master server
masters { 192.168.4.12; };
};
</programlisting>
</sect2>
</sect1>
<sect1>
<title>Load Balancing</title>
<!--
- Add explanation of why load balancing is fragile at best
- and completely pointless in the general case.
-->
<para>
A primitive form of load balancing can be achieved in
the <acronym>DNS</acronym> by using multiple records
(such as multiple A records) for one name.
</para>
<para>
For example, if you have three WWW servers with network addresses
of 10.0.0.1, 10.0.0.2 and 10.0.0.3, a set of records such as the
following means that clients will connect to each machine one third
of the time:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="5" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="0.500in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="0.750in"/>
<colspec colname="4" colnum="4" colsep="0" colwidth="0.750in"/>
<colspec colname="5" colnum="5" colsep="0" colwidth="2.028in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
Name
</para>
</entry>
<entry colname="2">
<para>
TTL
</para>
</entry>
<entry colname="3">
<para>
CLASS
</para>
</entry>
<entry colname="4">
<para>
TYPE
</para>
</entry>
<entry colname="5">
<para>
Resource Record (RR) Data
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>www</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>600</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>10.0.0.1</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>600</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>10.0.0.2</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>600</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>10.0.0.3</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
When a resolver queries for these records, <acronym>BIND</acronym> will rotate
them and respond to the query with the records in a different
order. In the example above, clients will randomly receive
records in the order 1, 2, 3; 2, 3, 1; and 3, 1, 2. Most clients
will use the first record returned and discard the rest.
</para>
<para>
For more detail on ordering responses, check the
<command>rrset-order</command> sub-statement in the
<command>options</command> statement, see
<xref endterm="rrset_ordering_title" linkend="rrset_ordering"/>.
</para>
</sect1>
<sect1>
<title>Name Server Operations</title>
<sect2>
<title>Tools for Use With the Name Server Daemon</title>
<para>
This section describes several indispensable diagnostic,
administrative and monitoring tools available to the system
administrator for controlling and debugging the name server
daemon.
</para>
<sect3 id="diagnostic_tools">
<title>Diagnostic Tools</title>
<para>
The <command>dig</command>, <command>host</command>, and
<command>nslookup</command> programs are all command
line tools
for manually querying name servers. They differ in style and
output format.
</para>
<variablelist>
<varlistentry>
<term id="dig"><command>dig</command></term>
<listitem>
<para>
The domain information groper (<command>dig</command>)
is the most versatile and complete of these lookup tools.
It has two modes: simple interactive
mode for a single query, and batch mode which executes a
query for
each in a list of several query lines. All query options are
accessible
from the command line.
</para>
<cmdsynopsis label="Usage">
<command>dig</command>
<arg>@<replaceable>server</replaceable></arg>
<arg choice="plain"><replaceable>domain</replaceable></arg>
<arg><replaceable>query-type</replaceable></arg>
<arg><replaceable>query-class</replaceable></arg>
<arg>+<replaceable>query-option</replaceable></arg>
<arg>-<replaceable>dig-option</replaceable></arg>
<arg>%<replaceable>comment</replaceable></arg>
</cmdsynopsis>
<para>
The usual simple use of <command>dig</command> will take the form
</para>
<simpara>
<command>dig @server domain query-type query-class</command>
</simpara>
<para>
For more information and a list of available commands and
options, see the <command>dig</command> man
page.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>host</command></term>
<listitem>
<para>
The <command>host</command> utility emphasizes
simplicity
and ease of use. By default, it converts
between host names and Internet addresses, but its
functionality
can be extended with the use of options.
</para>
<cmdsynopsis label="Usage">
<command>host</command>
<arg>-aCdlnrsTwv</arg>
<arg>-c <replaceable>class</replaceable></arg>
<arg>-N <replaceable>ndots</replaceable></arg>
<arg>-t <replaceable>type</replaceable></arg>
<arg>-W <replaceable>timeout</replaceable></arg>
<arg>-R <replaceable>retries</replaceable></arg>
<arg>-m <replaceable>flag</replaceable></arg>
<arg>-4</arg>
<arg>-6</arg>
<arg choice="plain"><replaceable>hostname</replaceable></arg>
<arg><replaceable>server</replaceable></arg>
</cmdsynopsis>
<para>
For more information and a list of available commands and
options, see the <command>host</command> man
page.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>nslookup</command></term>
<listitem>
<para><command>nslookup</command>
has two modes: interactive and
non-interactive. Interactive mode allows the user to
query name servers for information about various
hosts and domains or to print a list of hosts in a
domain. Non-interactive mode is used to print just
the name and requested information for a host or
domain.
</para>
<cmdsynopsis label="Usage">
<command>nslookup</command>
<arg rep="repeat">-option</arg>
<group>
<arg><replaceable>host-to-find</replaceable></arg>
<arg>- <arg>server</arg></arg>
</group>
</cmdsynopsis>
<para>
Interactive mode is entered when no arguments are given (the
default name server will be used) or when the first argument
is a
hyphen (`-') and the second argument is the host name or
Internet address
of a name server.
</para>
<para>
Non-interactive mode is used when the name or Internet
address
of the host to be looked up is given as the first argument.
The
optional second argument specifies the host name or address
of a name server.
</para>
<para>
Due to its arcane user interface and frequently inconsistent
behavior, we do not recommend the use of <command>nslookup</command>.
Use <command>dig</command> instead.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="admin_tools">
<title>Administrative Tools</title>
<para>
Administrative tools play an integral part in the management
of a server.
</para>
<variablelist>
<varlistentry id="named-checkconf" xreflabel="Named Configuration Checking application">
<term><command>named-checkconf</command></term>
<listitem>
<para>
The <command>named-checkconf</command> program
checks the syntax of a <filename>named.conf</filename> file.
</para>
<cmdsynopsis label="Usage">
<command>named-checkconf</command>
<arg>-jvz</arg>
<arg>-t <replaceable>directory</replaceable></arg>
<arg><replaceable>filename</replaceable></arg>
</cmdsynopsis>
</listitem>
</varlistentry>
<varlistentry id="named-checkzone" xreflabel="Zone Checking application">
<term><command>named-checkzone</command></term>
<listitem>
<para>
The <command>named-checkzone</command> program
checks a master file for
syntax and consistency.
</para>
<cmdsynopsis label="Usage">
<command>named-checkzone</command>
<arg>-djqvD</arg>
<arg>-c <replaceable>class</replaceable></arg>
<arg>-o <replaceable>output</replaceable></arg>
<arg>-t <replaceable>directory</replaceable></arg>
<arg>-w <replaceable>directory</replaceable></arg>
<arg>-k <replaceable>(ignore|warn|fail)</replaceable></arg>
<arg>-n <replaceable>(ignore|warn|fail)</replaceable></arg>
<arg>-W <replaceable>(ignore|warn)</replaceable></arg>
<arg choice="plain"><replaceable>zone</replaceable></arg>
<arg><replaceable>filename</replaceable></arg>
</cmdsynopsis>
</listitem>
</varlistentry>
<varlistentry id="named-compilezone" xreflabel="Zone Compilation application">
<term><command>named-compilezone</command></term>
<listitem>
<para>
Similar to <command>named-checkzone,</command> but
it always dumps the zone content to a specified file
(typically in a different format).
</para>
</listitem>
</varlistentry>
<varlistentry id="rndc" xreflabel="Remote Name Daemon Control application">
<term><command>rndc</command></term>
<listitem>
<para>
The remote name daemon control
(<command>rndc</command>) program allows the
system
administrator to control the operation of a name server.
Since <acronym>BIND</acronym> 9.2, <command>rndc</command>
supports all the commands of the BIND 8 <command>ndc</command>
utility except <command>ndc start</command> and
<command>ndc restart</command>, which were also
not supported in <command>ndc</command>'s
channel mode.
If you run <command>rndc</command> without any
options
it will display a usage message as follows:
</para>
<cmdsynopsis label="Usage">
<command>rndc</command>
<arg>-c <replaceable>config</replaceable></arg>
<arg>-s <replaceable>server</replaceable></arg>
<arg>-p <replaceable>port</replaceable></arg>
<arg>-y <replaceable>key</replaceable></arg>
<arg choice="plain"><replaceable>command</replaceable></arg>
<arg rep="repeat"><replaceable>command</replaceable></arg>
</cmdsynopsis>
<para>The <command>command</command>
is one of the following:
</para>
<variablelist>
<varlistentry>
<term><userinput>reload</userinput></term>
<listitem>
<para>
Reload configuration file and zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>reload <replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></userinput></term>
<listitem>
<para>
Reload the given zone.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>refresh <replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></userinput></term>
<listitem>
<para>
Schedule zone maintenance for the given zone.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>retransfer <replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></userinput></term>
<listitem>
<para>
Retransfer the given zone from the master.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>sign <replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></userinput></term>
<listitem>
<para>
Fetch all DNSSEC keys for the given zone
from the key directory (see
<command>key-directory</command> in
<xref linkend="options"/>). If they are within
their publication period, merge them into the
zone's DNSKEY RRset. If the DNSKEY RRset
is changed, then the zone is automatically
re-signed with the new key set.
</para>
<para>
This command requires that the
<command>auto-dnssec</command> zone option be set
to <literal>allow</literal> or
<literal>maintain</literal>,
and also requires the zone to be configured to
allow dynamic DNS.
See <xref linkend="dynamic_update_policies"/> for
more details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>loadkeys <replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></userinput></term>
<listitem>
<para>
Fetch all DNSSEC keys for the given zone
from the key directory (see
<command>key-directory</command> in
<xref linkend="options"/>). If they are within
their publication period, merge them into the
zone's DNSKEY RRset. Unlike <command>rndc
sign</command>, however, the zone is not
immediately re-signed by the new keys, but is
allowed to incrementally re-sign over time.
</para>
<para>
This command requires that the
<command>auto-dnssec</command> zone option
be set to <literal>maintain</literal>,
and also requires the zone to be configured to
allow dynamic DNS.
See <xref linkend="dynamic_update_policies"/> for
more details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>freeze
<optional><replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></optional></userinput></term>
<listitem>
<para>
Suspend updates to a dynamic zone. If no zone is
specified,
then all zones are suspended. This allows manual
edits to be made to a zone normally updated by dynamic
update. It
also causes changes in the journal file to be synced
into the master
and the journal file to be removed. All dynamic
update attempts will
be refused while the zone is frozen.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>thaw
<optional><replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></optional></userinput></term>
<listitem>
<para>
Enable updates to a frozen dynamic zone. If no zone
is
specified, then all frozen zones are enabled. This
causes
the server to reload the zone from disk, and
re-enables dynamic updates
after the load has completed. After a zone is thawed,
dynamic updates
will no longer be refused.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>notify <replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional></userinput></term>
<listitem>
<para>
Resend NOTIFY messages for the zone.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>reconfig</userinput></term>
<listitem>
<para>
Reload the configuration file and load new zones,
but do not reload existing zone files even if they
have changed.
This is faster than a full <command>reload</command> when there
is a large number of zones because it avoids the need
to examine the
modification times of the zones files.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>stats</userinput></term>
<listitem>
<para>
Write server statistics to the statistics file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>querylog</userinput></term>
<listitem>
<para>
Toggle query logging. Query logging can also be enabled
by explicitly directing the <command>queries</command>
<command>category</command> to a
<command>channel</command> in the
<command>logging</command> section of
<filename>named.conf</filename> or by specifying
<command>querylog yes;</command> in the
<command>options</command> section of
<filename>named.conf</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>dumpdb
<optional>-all|-cache|-zone</optional>
<optional><replaceable>view ...</replaceable></optional></userinput></term>
<listitem>
<para>
Dump the server's caches (default) and/or zones to
the
dump file for the specified views. If no view is
specified, all
views are dumped.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>secroots
<optional><replaceable>view ...</replaceable></optional></userinput></term>
<listitem>
<para>
Dump the server's security roots to the secroots
file for the specified views. If no view is
specified, security roots for all
views are dumped.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>stop <optional>-p</optional></userinput></term>
<listitem>
<para>
Stop the server, making sure any recent changes
made through dynamic update or IXFR are first saved to
the master files of the updated zones.
If <option>-p</option> is specified <command>named</command>'s process id is returned.
This allows an external process to determine when <command>named</command>
had completed stopping.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>halt <optional>-p</optional></userinput></term>
<listitem>
<para>
Stop the server immediately. Recent changes
made through dynamic update or IXFR are not saved to
the master files, but will be rolled forward from the
journal files when the server is restarted.
If <option>-p</option> is specified <command>named</command>'s process id is returned.
This allows an external process to determine when <command>named</command>
had completed halting.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>trace</userinput></term>
<listitem>
<para>
Increment the servers debugging level by one.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>trace <replaceable>level</replaceable></userinput></term>
<listitem>
<para>
Sets the server's debugging level to an explicit
value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>notrace</userinput></term>
<listitem>
<para>
Sets the server's debugging level to 0.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>flush</userinput></term>
<listitem>
<para>
Flushes the server's cache.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>flushname</userinput> <replaceable>name</replaceable></term>
<listitem>
<para>
Flushes the given name from the server's cache.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>status</userinput></term>
<listitem>
<para>
Display status of the server.
Note that the number of zones includes the internal <command>bind/CH</command> zone
and the default <command>./IN</command>
hint zone if there is not an
explicit root zone configured.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>recursing</userinput></term>
<listitem>
<para>
Dump the list of queries <command>named</command> is currently recursing
on.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>validation
<optional>on|off</optional>
<optional><replaceable>view ...</replaceable></optional>
</userinput></term>
<listitem>
<para>
Enable or disable DNSSEC validation.
Note <command>dnssec-enable</command> also needs to be
set to <userinput>yes</userinput> to be effective.
It defaults to enabled.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>tsig-list</userinput></term>
<listitem>
<para>
List the names of all TSIG keys currently configured
for use by <command>named</command> in each view. The
list both statically configured keys and dynamic
TKEY-negotiated keys.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>tsig-delete</userinput>
<replaceable>keyname</replaceable>
<optional><replaceable>view</replaceable></optional></term>
<listitem>
<para>
Delete a given TKEY-negotated key from the server.
(This does not apply to statically configured TSIG
keys.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>addzone
<replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional>
<replaceable>configuration</replaceable>
</userinput></term>
<listitem>
<para>
Add a zone while the server is running. This
command requires the
<command>allow-new-zones</command> option to be set
to <userinput>yes</userinput>. The
<replaceable>configuration</replaceable> string
specified on the command line is the zone
configuration text that would ordinarily be
placed in <filename>named.conf</filename>.
</para>
<para>
The configuration is saved in a file called
<filename><replaceable>hash</replaceable>.nzf</filename>,
where <replaceable>hash</replaceable> is a
cryptographic hash generated from the name of
the view. When <command>named</command> is
restarted, the file will be loaded into the view
configuration, so that zones that were added
can persist after a restart.
</para>
<para>
This sample <command>addzone</command> command
would add the zone <literal>example.com</literal>
to the default view:
</para>
<para>
<prompt>$ </prompt><userinput>rndc addzone example.com '{ type master; file "example.com.db"; };'</userinput>
</para>
<para>
(Note the brackets and semi-colon around the zone
configuration text.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><userinput>delzone
<replaceable>zone</replaceable>
<optional><replaceable>class</replaceable>
<optional><replaceable>view</replaceable></optional></optional>
</userinput></term>
<listitem>
<para>
Delete a zone while the server is running.
Only zones that were originally added via
<command>rndc addzone</command> can be deleted
in this matter.
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
A configuration file is required, since all
communication with the server is authenticated with
digital signatures that rely on a shared secret, and
there is no way to provide that secret other than with a
configuration file. The default location for the
<command>rndc</command> configuration file is
<filename>/etc/rndc.conf</filename>, but an
alternate
location can be specified with the <option>-c</option>
option. If the configuration file is not found,
<command>rndc</command> will also look in
<filename>/etc/rndc.key</filename> (or whatever
<varname>sysconfdir</varname> was defined when
the <acronym>BIND</acronym> build was
configured).
The <filename>rndc.key</filename> file is
generated by
running <command>rndc-confgen -a</command> as
described in
<xref linkend="controls_statement_definition_and_usage"/>.
</para>
<para>
The format of the configuration file is similar to
that of <filename>named.conf</filename>, but
limited to
only four statements, the <command>options</command>,
<command>key</command>, <command>server</command> and
<command>include</command>
statements. These statements are what associate the
secret keys to the servers with which they are meant to
be shared. The order of statements is not
significant.
</para>
<para>
The <command>options</command> statement has
three clauses:
<command>default-server</command>, <command>default-key</command>,
and <command>default-port</command>.
<command>default-server</command> takes a
host name or address argument and represents the server
that will
be contacted if no <option>-s</option>
option is provided on the command line.
<command>default-key</command> takes
the name of a key as its argument, as defined by a <command>key</command> statement.
<command>default-port</command> specifies the
port to which
<command>rndc</command> should connect if no
port is given on the command line or in a
<command>server</command> statement.
</para>
<para>
The <command>key</command> statement defines a
key to be used
by <command>rndc</command> when authenticating
with
<command>named</command>. Its syntax is
identical to the
<command>key</command> statement in <filename>named.conf</filename>.
The keyword <userinput>key</userinput> is
followed by a key name, which must be a valid
domain name, though it need not actually be hierarchical;
thus,
a string like "<userinput>rndc_key</userinput>" is a valid
name.
The <command>key</command> statement has two
clauses:
<command>algorithm</command> and <command>secret</command>.
While the configuration parser will accept any string as the
argument
to algorithm, currently only the string "<userinput>hmac-md5</userinput>"
has any meaning. The secret is a base-64 encoded string
as specified in RFC 3548.
</para>
<para>
The <command>server</command> statement
associates a key
defined using the <command>key</command>
statement with a server.
The keyword <userinput>server</userinput> is followed by a
host name or address. The <command>server</command> statement
has two clauses: <command>key</command> and <command>port</command>.
The <command>key</command> clause specifies the
name of the key
to be used when communicating with this server, and the
<command>port</command> clause can be used to
specify the port <command>rndc</command> should
connect
to on the server.
</para>
<para>
A sample minimal configuration file is as follows:
</para>
<programlisting>
key rndc_key {
algorithm "hmac-md5";
secret
"c3Ryb25nIGVub3VnaCBmb3IgYSBtYW4gYnV0IG1hZGUgZm9yIGEgd29tYW4K";
};
options {
default-server 127.0.0.1;
default-key rndc_key;
};
</programlisting>
<para>
This file, if installed as <filename>/etc/rndc.conf</filename>,
would allow the command:
</para>
<para>
<prompt>$ </prompt><userinput>rndc reload</userinput>
</para>
<para>
to connect to 127.0.0.1 port 953 and cause the name server
to reload, if a name server on the local machine were
running with
following controls statements:
</para>
<programlisting>
controls {
inet 127.0.0.1
allow { localhost; } keys { rndc_key; };
};
</programlisting>
<para>
and it had an identical key statement for
<literal>rndc_key</literal>.
</para>
<para>
Running the <command>rndc-confgen</command>
program will
conveniently create a <filename>rndc.conf</filename>
file for you, and also display the
corresponding <command>controls</command>
statement that you need to
add to <filename>named.conf</filename>.
Alternatively,
you can run <command>rndc-confgen -a</command>
to set up
a <filename>rndc.key</filename> file and not
modify
<filename>named.conf</filename> at all.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
</sect2>
<sect2>
<title>Signals</title>
<para>
Certain UNIX signals cause the name server to take specific
actions, as described in the following table. These signals can
be sent using the <command>kill</command> command.
</para>
<informaltable frame="all">
<tgroup cols="2">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.125in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>SIGHUP</command></para>
</entry>
<entry colname="2">
<para>
Causes the server to read <filename>named.conf</filename> and
reload the database.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SIGTERM</command></para>
</entry>
<entry colname="2">
<para>
Causes the server to clean up and exit.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SIGINT</command></para>
</entry>
<entry colname="2">
<para>
Causes the server to clean up and exit.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect2>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch04">
<title>Advanced DNS Features</title>
<sect1 id="notify">
<title>Notify</title>
<para>
<acronym>DNS</acronym> NOTIFY is a mechanism that allows master
servers to notify their slave servers of changes to a zone's data. In
response to a <command>NOTIFY</command> from a master server, the
slave will check to see that its version of the zone is the
current version and, if not, initiate a zone transfer.
</para>
<para>
For more information about <acronym>DNS</acronym>
<command>NOTIFY</command>, see the description of the
<command>notify</command> option in <xref linkend="boolean_options"/> and
the description of the zone option <command>also-notify</command> in
<xref linkend="zone_transfers"/>. The <command>NOTIFY</command>
protocol is specified in RFC 1996.
</para>
<note>
As a slave zone can also be a master to other slaves, <command>named</command>,
by default, sends <command>NOTIFY</command> messages for every zone
it loads. Specifying <command>notify master-only;</command> will
cause <command>named</command> to only send <command>NOTIFY</command> for master
zones that it loads.
</note>
</sect1>
<sect1 id="dynamic_update">
<title>Dynamic Update</title>
<para>
Dynamic Update is a method for adding, replacing or deleting
records in a master server by sending it a special form of DNS
messages. The format and meaning of these messages is specified
in RFC 2136.
</para>
<para>
Dynamic update is enabled by including an
<command>allow-update</command> or an <command>update-policy</command>
clause in the <command>zone</command> statement.
</para>
<para>
If the zone's <command>update-policy</command> is set to
<userinput>local</userinput>, updates to the zone
will be permitted for the key <varname>local-ddns</varname>,
which will be generated by <command>named</command> at startup.
See <xref linkend="dynamic_update_policies"/> for more details.
</para>
<para>
Dynamic updates using Kerberos signed requests can be made
using the TKEY/GSS protocol by setting either the
<command>tkey-gssapi-keytab</command> option, or alternatively
by setting both the <command>tkey-gssapi-credential</command>
and <command>tkey-domain</command> options. Once enabled,
Kerberos signed requests will be matched against the update
policies for the zone, using the Kerberos principal as the
signer for the request.
</para>
<para>
Updating of secure zones (zones using DNSSEC) follows RFC
3007: RRSIG, NSEC and NSEC3 records affected by updates are
automatically regenerated by the server using an online
zone key. Update authorization is based on transaction
signatures and an explicit server policy.
</para>
<sect2 id="journal">
<title>The journal file</title>
<para>
All changes made to a zone using dynamic update are stored
in the zone's journal file. This file is automatically created
by the server when the first dynamic update takes place.
The name of the journal file is formed by appending the extension
<filename>.jnl</filename> to the name of the
corresponding zone
file unless specifically overridden. The journal file is in a
binary format and should not be edited manually.
</para>
<para>
The server will also occasionally write ("dump")
the complete contents of the updated zone to its zone file.
This is not done immediately after
each dynamic update, because that would be too slow when a large
zone is updated frequently. Instead, the dump is delayed by
up to 15 minutes, allowing additional updates to take place.
During the dump process, transient files will be created
with the extensions <filename>.jnw</filename> and
<filename>.jbk</filename>; under ordinary circumstances, these
will be removed when the dump is complete, and can be safely
ignored.
</para>
<para>
When a server is restarted after a shutdown or crash, it will replay
the journal file to incorporate into the zone any updates that
took
place after the last zone dump.
</para>
<para>
Changes that result from incoming incremental zone transfers are
also
journalled in a similar way.
</para>
<para>
The zone files of dynamic zones cannot normally be edited by
hand because they are not guaranteed to contain the most recent
dynamic changes — those are only in the journal file.
The only way to ensure that the zone file of a dynamic zone
is up to date is to run <command>rndc stop</command>.
</para>
<para>
If you have to make changes to a dynamic zone
manually, the following procedure will work: Disable dynamic updates
to the zone using
<command>rndc freeze <replaceable>zone</replaceable></command>.
This will also remove the zone's <filename>.jnl</filename> file
and update the master file. Edit the zone file. Run
<command>rndc thaw <replaceable>zone</replaceable></command>
to reload the changed zone and re-enable dynamic updates.
</para>
</sect2>
</sect1>
<sect1 id="incremental_zone_transfers">
<title>Incremental Zone Transfers (IXFR)</title>
<para>
The incremental zone transfer (IXFR) protocol is a way for
slave servers to transfer only changed data, instead of having to
transfer the entire zone. The IXFR protocol is specified in RFC
1995. See <xref linkend="proposed_standards"/>.
</para>
<para>
When acting as a master, <acronym>BIND</acronym> 9
supports IXFR for those zones
where the necessary change history information is available. These
include master zones maintained by dynamic update and slave zones
whose data was obtained by IXFR. For manually maintained master
zones, and for slave zones obtained by performing a full zone
transfer (AXFR), IXFR is supported only if the option
<command>ixfr-from-differences</command> is set
to <userinput>yes</userinput>.
</para>
<para>
When acting as a slave, <acronym>BIND</acronym> 9 will attempt
to use IXFR unless it is explicitly disabled via the
<command>request-ixfr</command> option or the use of
<command>ixfr-from-differences</command>. For
more information about disabling IXFR, see the description
of the <command>request-ixfr</command> clause of the
<command>server</command> statement.
</para>
</sect1>
<sect1>
<title>Split DNS</title>
<para>
Setting up different views, or visibility, of the DNS space to
internal and external resolvers is usually referred to as a
<emphasis>Split DNS</emphasis> setup. There are several
reasons an organization would want to set up its DNS this way.
</para>
<para>
One common reason for setting up a DNS system this way is
to hide "internal" DNS information from "external" clients on the
Internet. There is some debate as to whether or not this is actually
useful.
Internal DNS information leaks out in many ways (via email headers,
for example) and most savvy "attackers" can find the information
they need using other means.
However, since listing addresses of internal servers that
external clients cannot possibly reach can result in
connection delays and other annoyances, an organization may
choose to use a Split DNS to present a consistent view of itself
to the outside world.
</para>
<para>
Another common reason for setting up a Split DNS system is
to allow internal networks that are behind filters or in RFC 1918
space (reserved IP space, as documented in RFC 1918) to resolve DNS
on the Internet. Split DNS can also be used to allow mail from outside
back in to the internal network.
</para>
<sect2>
<title>Example split DNS setup</title>
<para>
Let's say a company named <emphasis>Example, Inc.</emphasis>
(<literal>example.com</literal>)
has several corporate sites that have an internal network with
reserved
Internet Protocol (IP) space and an external demilitarized zone (DMZ),
or "outside" section of a network, that is available to the public.
</para>
<para>
<emphasis>Example, Inc.</emphasis> wants its internal clients
to be able to resolve external hostnames and to exchange mail with
people on the outside. The company also wants its internal resolvers
to have access to certain internal-only zones that are not available
at all outside of the internal network.
</para>
<para>
In order to accomplish this, the company will set up two sets
of name servers. One set will be on the inside network (in the
reserved
IP space) and the other set will be on bastion hosts, which are
"proxy"
hosts that can talk to both sides of its network, in the DMZ.
</para>
<para>
The internal servers will be configured to forward all queries,
except queries for <filename>site1.internal</filename>, <filename>site2.internal</filename>, <filename>site1.example.com</filename>,
and <filename>site2.example.com</filename>, to the servers
in the
DMZ. These internal servers will have complete sets of information
for <filename>site1.example.com</filename>, <filename>site2.example.com</filename>, <filename>site1.internal</filename>,
and <filename>site2.internal</filename>.
</para>
<para>
To protect the <filename>site1.internal</filename> and <filename>site2.internal</filename> domains,
the internal name servers must be configured to disallow all queries
to these domains from any external hosts, including the bastion
hosts.
</para>
<para>
The external servers, which are on the bastion hosts, will
be configured to serve the "public" version of the <filename>site1</filename> and <filename>site2.example.com</filename> zones.
This could include things such as the host records for public servers
(<filename>www.example.com</filename> and <filename>ftp.example.com</filename>),
and mail exchange (MX) records (<filename>a.mx.example.com</filename> and <filename>b.mx.example.com</filename>).
</para>
<para>
In addition, the public <filename>site1</filename> and <filename>site2.example.com</filename> zones
should have special MX records that contain wildcard (`*') records
pointing to the bastion hosts. This is needed because external mail
servers do not have any other way of looking up how to deliver mail
to those internal hosts. With the wildcard records, the mail will
be delivered to the bastion host, which can then forward it on to
internal hosts.
</para>
<para>
Here's an example of a wildcard MX record:
</para>
<programlisting>* IN MX 10 external1.example.com.</programlisting>
<para>
Now that they accept mail on behalf of anything in the internal
network, the bastion hosts will need to know how to deliver mail
to internal hosts. In order for this to work properly, the resolvers
on
the bastion hosts will need to be configured to point to the internal
name servers for DNS resolution.
</para>
<para>
Queries for internal hostnames will be answered by the internal
servers, and queries for external hostnames will be forwarded back
out to the DNS servers on the bastion hosts.
</para>
<para>
In order for all this to work properly, internal clients will
need to be configured to query <emphasis>only</emphasis> the internal
name servers for DNS queries. This could also be enforced via
selective
filtering on the network.
</para>
<para>
If everything has been set properly, <emphasis>Example, Inc.</emphasis>'s
internal clients will now be able to:
</para>
<itemizedlist>
<listitem>
<simpara>
Look up any hostnames in the <literal>site1</literal>
and
<literal>site2.example.com</literal> zones.
</simpara>
</listitem>
<listitem>
<simpara>
Look up any hostnames in the <literal>site1.internal</literal> and
<literal>site2.internal</literal> domains.
</simpara>
</listitem>
<listitem>
<simpara>Look up any hostnames on the Internet.</simpara>
</listitem>
<listitem>
<simpara>Exchange mail with both internal and external people.</simpara>
</listitem>
</itemizedlist>
<para>
Hosts on the Internet will be able to:
</para>
<itemizedlist>
<listitem>
<simpara>
Look up any hostnames in the <literal>site1</literal>
and
<literal>site2.example.com</literal> zones.
</simpara>
</listitem>
<listitem>
<simpara>
Exchange mail with anyone in the <literal>site1</literal> and
<literal>site2.example.com</literal> zones.
</simpara>
</listitem>
</itemizedlist>
<para>
Here is an example configuration for the setup we just
described above. Note that this is only configuration information;
for information on how to configure your zone files, see <xref linkend="sample_configuration"/>.
</para>
<para>
Internal DNS server config:
</para>
<programlisting>
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { <varname>bastion-ips-go-here</varname>; };
options {
...
...
forward only;
// forward to external servers
forwarders {
<varname>bastion-ips-go-here</varname>;
};
// sample allow-transfer (no one)
allow-transfer { none; };
// restrict query access
allow-query { internals; externals; };
// restrict recursion
allow-recursion { internals; };
...
...
};
// sample master zone
zone "site1.example.com" {
type master;
file "m/site1.example.com";
// do normal iterative resolution (do not forward)
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
// sample slave zone
zone "site2.example.com" {
type slave;
file "s/site2.example.com";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals; externals; };
allow-transfer { internals; };
};
zone "site1.internal" {
type master;
file "m/site1.internal";
forwarders { };
allow-query { internals; };
allow-transfer { internals; }
};
zone "site2.internal" {
type slave;
file "s/site2.internal";
masters { 172.16.72.3; };
forwarders { };
allow-query { internals };
allow-transfer { internals; }
};
</programlisting>
<para>
External (bastion host) DNS server config:
</para>
<programlisting>
acl internals { 172.16.72.0/24; 192.168.1.0/24; };
acl externals { bastion-ips-go-here; };
options {
...
...
// sample allow-transfer (no one)
allow-transfer { none; };
// default query access
allow-query { any; };
// restrict cache access
allow-query-cache { internals; externals; };
// restrict recursion
allow-recursion { internals; externals; };
...
...
};
// sample slave zone
zone "site1.example.com" {
type master;
file "m/site1.foo.com";
allow-transfer { internals; externals; };
};
zone "site2.example.com" {
type slave;
file "s/site2.foo.com";
masters { another_bastion_host_maybe; };
allow-transfer { internals; externals; }
};
</programlisting>
<para>
In the <filename>resolv.conf</filename> (or equivalent) on
the bastion host(s):
</para>
<programlisting>
search ...
nameserver 172.16.72.2
nameserver 172.16.72.3
nameserver 172.16.72.4
</programlisting>
</sect2>
</sect1>
<sect1 id="tsig">
<title>TSIG</title>
<para>
This is a short guide to setting up Transaction SIGnatures
(TSIG) based transaction security in <acronym>BIND</acronym>. It describes changes
to the configuration file as well as what changes are required for
different features, including the process of creating transaction
keys and using transaction signatures with <acronym>BIND</acronym>.
</para>
<para>
<acronym>BIND</acronym> primarily supports TSIG for server
to server communication.
This includes zone transfer, notify, and recursive query messages.
Resolvers based on newer versions of <acronym>BIND</acronym> 8 have limited support
for TSIG.
</para>
<para>
TSIG can also be useful for dynamic update. A primary
server for a dynamic zone should control access to the dynamic
update service, but IP-based access control is insufficient.
The cryptographic access control provided by TSIG
is far superior. The <command>nsupdate</command>
program supports TSIG via the <option>-k</option> and
<option>-y</option> command line options or inline by use
of the <command>key</command>.
</para>
<sect2>
<title>Generate Shared Keys for Each Pair of Hosts</title>
<para>
A shared secret is generated to be shared between <emphasis>host1</emphasis> and <emphasis>host2</emphasis>.
An arbitrary key name is chosen: "host1-host2.". The key name must
be the same on both hosts.
</para>
<sect3>
<title>Automatic Generation</title>
<para>
The following command will generate a 128-bit (16 byte) HMAC-SHA256
key as described above. Longer keys are better, but shorter keys
are easier to read. Note that the maximum key length is the digest
length, here 256 bits.
</para>
<para>
<userinput>dnssec-keygen -a hmac-sha256 -b 128 -n HOST host1-host2.</userinput>
</para>
<para>
The key is in the file <filename>Khost1-host2.+163+00000.private</filename>.
Nothing directly uses this file, but the base-64 encoded string
following "<literal>Key:</literal>"
can be extracted from the file and used as a shared secret:
</para>
<programlisting>Key: La/E5CjG9O+os1jq0a2jdA==</programlisting>
<para>
The string "<literal>La/E5CjG9O+os1jq0a2jdA==</literal>" can
be used as the shared secret.
</para>
</sect3>
<sect3>
<title>Manual Generation</title>
<para>
The shared secret is simply a random sequence of bits, encoded
in base-64. Most ASCII strings are valid base-64 strings (assuming
the length is a multiple of 4 and only valid characters are used),
so the shared secret can be manually generated.
</para>
<para>
Also, a known string can be run through <command>mmencode</command> or
a similar program to generate base-64 encoded data.
</para>
</sect3>
</sect2>
<sect2>
<title>Copying the Shared Secret to Both Machines</title>
<para>
This is beyond the scope of DNS. A secure transport mechanism
should be used. This could be secure FTP, ssh, telephone, etc.
</para>
</sect2>
<sect2>
<title>Informing the Servers of the Key's Existence</title>
<para>
Imagine <emphasis>host1</emphasis> and <emphasis>host 2</emphasis>
are
both servers. The following is added to each server's <filename>named.conf</filename> file:
</para>
<programlisting>
key host1-host2. {
algorithm hmac-sha256;
secret "La/E5CjG9O+os1jq0a2jdA==";
};
</programlisting>
<para>
The secret is the one generated above. Since this is a secret, it
is recommended that either <filename>named.conf</filename> be
non-world readable, or the key directive be added to a non-world
readable file that is included by <filename>named.conf</filename>.
</para>
<para>
At this point, the key is recognized. This means that if the
server receives a message signed by this key, it can verify the
signature. If the signature is successfully verified, the
response is signed by the same key.
</para>
</sect2>
<sect2>
<title>Instructing the Server to Use the Key</title>
<para>
Since keys are shared between two hosts only, the server must
be told when keys are to be used. The following is added to the <filename>named.conf</filename> file
for <emphasis>host1</emphasis>, if the IP address of <emphasis>host2</emphasis> is
10.1.2.3:
</para>
<programlisting>
server 10.1.2.3 {
keys { host1-host2. ;};
};
</programlisting>
<para>
Multiple keys may be present, but only the first is used.
This directive does not contain any secrets, so it may be in a
world-readable
file.
</para>
<para>
If <emphasis>host1</emphasis> sends a message that is a request
to that address, the message will be signed with the specified key. <emphasis>host1</emphasis> will
expect any responses to signed messages to be signed with the same
key.
</para>
<para>
A similar statement must be present in <emphasis>host2</emphasis>'s
configuration file (with <emphasis>host1</emphasis>'s address) for <emphasis>host2</emphasis> to
sign request messages to <emphasis>host1</emphasis>.
</para>
</sect2>
<sect2>
<title>TSIG Key Based Access Control</title>
<para>
<acronym>BIND</acronym> allows IP addresses and ranges
to be specified in ACL
definitions and
<command>allow-{ query | transfer | update }</command>
directives.
This has been extended to allow TSIG keys also. The above key would
be denoted <command>key host1-host2.</command>
</para>
<para>
An example of an <command>allow-update</command> directive would be:
</para>
<programlisting>
allow-update { key host1-host2. ;};
</programlisting>
<para>
This allows dynamic updates to succeed only if the request
was signed by a key named "<command>host1-host2.</command>".
</para>
<para>
See <xref linkend="dynamic_update_policies"/> for a discussion of
the more flexible <command>update-policy</command> statement.
</para>
</sect2>
<sect2>
<title>Errors</title>
<para>
The processing of TSIG signed messages can result in
several errors. If a signed message is sent to a non-TSIG aware
server, a FORMERR (format error) will be returned, since the server will not
understand the record. This is a result of misconfiguration,
since the server must be explicitly configured to send a TSIG
signed message to a specific server.
</para>
<para>
If a TSIG aware server receives a message signed by an
unknown key, the response will be unsigned with the TSIG
extended error code set to BADKEY. If a TSIG aware server
receives a message with a signature that does not validate, the
response will be unsigned with the TSIG extended error code set
to BADSIG. If a TSIG aware server receives a message with a time
outside of the allowed range, the response will be signed with
the TSIG extended error code set to BADTIME, and the time values
will be adjusted so that the response can be successfully
verified. In any of these cases, the message's rcode (response code) is set to
NOTAUTH (not authenticated).
</para>
</sect2>
</sect1>
<sect1>
<title>TKEY</title>
<para><command>TKEY</command>
is a mechanism for automatically generating a shared secret
between two hosts. There are several "modes" of
<command>TKEY</command> that specify how the key is generated
or assigned. <acronym>BIND</acronym> 9 implements only one of
these modes, the Diffie-Hellman key exchange. Both hosts are
required to have a Diffie-Hellman KEY record (although this
record is not required to be present in a zone). The
<command>TKEY</command> process must use signed messages,
signed either by TSIG or SIG(0). The result of
<command>TKEY</command> is a shared secret that can be used to
sign messages with TSIG. <command>TKEY</command> can also be
used to delete shared secrets that it had previously
generated.
</para>
<para>
The <command>TKEY</command> process is initiated by a
client
or server by sending a signed <command>TKEY</command>
query
(including any appropriate KEYs) to a TKEY-aware server. The
server response, if it indicates success, will contain a
<command>TKEY</command> record and any appropriate keys.
After
this exchange, both participants have enough information to
determine the shared secret; the exact process depends on the
<command>TKEY</command> mode. When using the
Diffie-Hellman
<command>TKEY</command> mode, Diffie-Hellman keys are
exchanged,
and the shared secret is derived by both participants.
</para>
</sect1>
<sect1>
<title>SIG(0)</title>
<para>
<acronym>BIND</acronym> 9 partially supports DNSSEC SIG(0)
transaction signatures as specified in RFC 2535 and RFC 2931.
SIG(0)
uses public/private keys to authenticate messages. Access control
is performed in the same manner as TSIG keys; privileges can be
granted or denied based on the key name.
</para>
<para>
When a SIG(0) signed message is received, it will only be
verified if the key is known and trusted by the server; the server
will not attempt to locate and/or validate the key.
</para>
<para>
SIG(0) signing of multiple-message TCP streams is not
supported.
</para>
<para>
The only tool shipped with <acronym>BIND</acronym> 9 that
generates SIG(0) signed messages is <command>nsupdate</command>.
</para>
</sect1>
<sect1 id="DNSSEC">
<title>DNSSEC</title>
<para>
Cryptographic authentication of DNS information is possible
through the DNS Security (<emphasis>DNSSEC-bis</emphasis>) extensions,
defined in RFC 4033, RFC 4034, and RFC 4035.
This section describes the creation and use of DNSSEC signed zones.
</para>
<para>
In order to set up a DNSSEC secure zone, there are a series
of steps which must be followed. <acronym>BIND</acronym>
9 ships
with several tools
that are used in this process, which are explained in more detail
below. In all cases, the <option>-h</option> option prints a
full list of parameters. Note that the DNSSEC tools require the
keyset files to be in the working directory or the
directory specified by the <option>-d</option> option, and
that the tools shipped with BIND 9.2.x and earlier are not compatible
with the current ones.
</para>
<para>
There must also be communication with the administrators of
the parent and/or child zone to transmit keys. A zone's security
status must be indicated by the parent zone for a DNSSEC capable
resolver to trust its data. This is done through the presence
or absence of a <literal>DS</literal> record at the
delegation
point.
</para>
<para>
For other servers to trust data in this zone, they must
either be statically configured with this zone's zone key or the
zone key of another zone above this one in the DNS tree.
</para>
<sect2>
<title>Generating Keys</title>
<para>
The <command>dnssec-keygen</command> program is used to
generate keys.
</para>
<para>
A secure zone must contain one or more zone keys. The
zone keys will sign all other records in the zone, as well as
the zone keys of any secure delegated zones. Zone keys must
have the same name as the zone, a name type of
<command>ZONE</command>, and must be usable for
authentication.
It is recommended that zone keys use a cryptographic algorithm
designated as "mandatory to implement" by the IETF; currently
the only one is RSASHA1.
</para>
<para>
The following command will generate a 768-bit RSASHA1 key for
the <filename>child.example</filename> zone:
</para>
<para>
<userinput>dnssec-keygen -a RSASHA1 -b 768 -n ZONE child.example.</userinput>
</para>
<para>
Two output files will be produced:
<filename>Kchild.example.+005+12345.key</filename> and
<filename>Kchild.example.+005+12345.private</filename>
(where
12345 is an example of a key tag). The key filenames contain
the key name (<filename>child.example.</filename>),
algorithm (3
is DSA, 1 is RSAMD5, 5 is RSASHA1, etc.), and the key tag (12345 in
this case).
The private key (in the <filename>.private</filename>
file) is
used to generate signatures, and the public key (in the
<filename>.key</filename> file) is used for signature
verification.
</para>
<para>
To generate another key with the same properties (but with
a different key tag), repeat the above command.
</para>
<para>
The <command>dnssec-keyfromlabel</command> program is used
to get a key pair from a crypto hardware and build the key
files. Its usage is similar to <command>dnssec-keygen</command>.
</para>
<para>
The public keys should be inserted into the zone file by
including the <filename>.key</filename> files using
<command>$INCLUDE</command> statements.
</para>
</sect2>
<sect2>
<title>Signing the Zone</title>
<para>
The <command>dnssec-signzone</command> program is used
to sign a zone.
</para>
<para>
Any <filename>keyset</filename> files corresponding to
secure subzones should be present. The zone signer will
generate <literal>NSEC</literal>, <literal>NSEC3</literal>
and <literal>RRSIG</literal> records for the zone, as
well as <literal>DS</literal> for the child zones if
<literal>'-g'</literal> is specified. If <literal>'-g'</literal>
is not specified, then DS RRsets for the secure child
zones need to be added manually.
</para>
<para>
The following command signs the zone, assuming it is in a
file called <filename>zone.child.example</filename>. By
default, all zone keys which have an available private key are
used to generate signatures.
</para>
<para>
<userinput>dnssec-signzone -o child.example zone.child.example</userinput>
</para>
<para>
One output file is produced:
<filename>zone.child.example.signed</filename>. This
file
should be referenced by <filename>named.conf</filename>
as the
input file for the zone.
</para>
<para><command>dnssec-signzone</command>
will also produce a keyset and dsset files and optionally a
dlvset file. These are used to provide the parent zone
administrators with the <literal>DNSKEYs</literal> (or their
corresponding <literal>DS</literal> records) that are the
secure entry point to the zone.
</para>
</sect2>
<sect2>
<title>Configuring Servers</title>
<para>
To enable <command>named</command> to respond appropriately
to DNS requests from DNSSEC aware clients,
<command>dnssec-enable</command> must be set to yes.
(This is the default setting.)
</para>
<para>
To enable <command>named</command> to validate answers from
other servers, the <command>dnssec-enable</command> option
must be set to <userinput>yes</userinput>, and the
<command>dnssec-validation</command> options must be set to
<userinput>yes</userinput> or <userinput>auto</userinput>.
</para>
<para>
If <command>dnssec-validation</command> is set to
<userinput>auto</userinput>, then a default
trust anchor for the DNS root zone will be used.
If it is set to <userinput>yes</userinput>, however,
then at least one trust anchor must be configured
with a <command>trusted-keys</command> or
<command>managed-keys</command> statement in
<filename>named.conf</filename>, or DNSSEC validation
will not occur. The default setting is
<userinput>yes</userinput>.
</para>
<para>
<command>trusted-keys</command> are copies of DNSKEY RRs
for zones that are used to form the first link in the
cryptographic chain of trust. All keys listed in
<command>trusted-keys</command> (and corresponding zones)
are deemed to exist and only the listed keys will be used
to validated the DNSKEY RRset that they are from.
</para>
<para>
<command>managed-keys</command> are trusted keys which are
automatically kept up to date via RFC 5011 trust anchor
maintenance.
</para>
<para>
<command>trusted-keys</command> and
<command>managed-keys</command> are described in more detail
later in this document.
</para>
<para>
Unlike <acronym>BIND</acronym> 8, <acronym>BIND</acronym>
9 does not verify signatures on load, so zone keys for
authoritative zones do not need to be specified in the
configuration file.
</para>
<para>
After DNSSEC gets established, a typical DNSSEC configuration
will look something like the following. It has one or
more public keys for the root. This allows answers from
outside the organization to be validated. It will also
have several keys for parts of the namespace the organization
controls. These are here to ensure that <command>named</command>
is immune to compromises in the DNSSEC components of the security
of parent zones.
</para>
<programlisting>
managed-keys {
/* Root Key */
"." initial-key 257 3 3 "BNY4wrWM1nCfJ+CXd0rVXyYmobt7sEEfK3clRbGaTwS
JxrGkxJWoZu6I7PzJu/E9gx4UC1zGAHlXKdE4zYIpRh
aBKnvcC2U9mZhkdUpd1Vso/HAdjNe8LmMlnzY3zy2Xy
4klWOADTPzSv9eamj8V18PHGjBLaVtYvk/ln5ZApjYg
hf+6fElrmLkdaz MQ2OCnACR817DF4BBa7UR/beDHyp
5iWTXWSi6XmoJLbG9Scqc7l70KDqlvXR3M/lUUVRbke
g1IPJSidmK3ZyCllh4XSKbje/45SKucHgnwU5jefMtq
66gKodQj+MiA21AfUVe7u99WzTLzY3qlxDhxYQQ20FQ
97S+LKUTpQcq27R7AT3/V5hRQxScINqwcz4jYqZD2fQ
dgxbcDTClU0CRBdiieyLMNzXG3";
};
trusted-keys {
/* Key for our organization's forward zone */
example.com. 257 3 5 "AwEAAaxPMcR2x0HbQV4WeZB6oEDX+r0QM6
5KbhTjrW1ZaARmPhEZZe3Y9ifgEuq7vZ/z
GZUdEGNWy+JZzus0lUptwgjGwhUS1558Hb
4JKUbbOTcM8pwXlj0EiX3oDFVmjHO444gL
kBOUKUf/mC7HvfwYH/Be22GnClrinKJp1O
g4ywzO9WglMk7jbfW33gUKvirTHr25GL7S
TQUzBb5Usxt8lgnyTUHs1t3JwCY5hKZ6Cq
FxmAVZP20igTixin/1LcrgX/KMEGd/biuv
F4qJCyduieHukuY3H4XMAcR+xia2nIUPvm
/oyWR8BW/hWdzOvnSCThlHf3xiYleDbt/o
1OTQ09A0=";
/* Key for our reverse zone. */
2.0.192.IN-ADDRPA.NET. 257 3 5 "AQOnS4xn/IgOUpBPJ3bogzwc
xOdNax071L18QqZnQQQAVVr+i
LhGTnNGp3HoWQLUIzKrJVZ3zg
gy3WwNT6kZo6c0tszYqbtvchm
gQC8CzKojM/W16i6MG/eafGU3
siaOdS0yOI6BgPsw+YZdzlYMa
IJGf4M4dyoKIhzdZyQ2bYQrjy
Q4LB0lC7aOnsMyYKHHYeRvPxj
IQXmdqgOJGq+vsevG06zW+1xg
YJh9rCIfnm1GX/KMgxLPG2vXT
D/RnLX+D3T3UL7HJYHJhAZD5L
59VvjSPsZJHeDCUyWYrvPZesZ
DIRvhDD52SKvbheeTJUm6Ehkz
ytNN2SN96QRk8j/iI8ib";
};
options {
...
dnssec-enable yes;
dnssec-validation yes;
};
</programlisting>
<note>
None of the keys listed in this example are valid. In particular,
the root key is not valid.
</note>
<para>
When DNSSEC validation is enabled and properly configured,
the resolver will reject any answers from signed, secure zones
which fail to validate, and will return SERVFAIL to the client.
</para>
<para>
Responses may fail to validate for any of several reasons,
including missing, expired, or invalid signatures, a key which
does not match the DS RRset in the parent zone, or an insecure
response from a zone which, according to its parent, should have
been secure.
</para>
<note>
<para>
When the validator receives a response from an unsigned zone
that has a signed parent, it must confirm with the parent
that the zone was intentionally left unsigned. It does
this by verifying, via signed and validated NSEC/NSEC3 records,
that the parent zone contains no DS records for the child.
</para>
<para>
If the validator <emphasis>can</emphasis> prove that the zone
is insecure, then the response is accepted. However, if it
cannot, then it must assume an insecure response to be a
forgery; it rejects the response and logs an error.
</para>
<para>
The logged error reads "insecurity proof failed" and
"got insecure response; parent indicates it should be secure".
(Prior to BIND 9.7, the logged error was "not insecure".
This referred to the zone, not the response.)
</para>
</note>
</sect2>
</sect1>
<xi:include href="dnssec.xml"/>
<xi:include href="managed-keys.xml"/>
<xi:include href="pkcs11.xml"/>
<sect1>
<title>IPv6 Support in <acronym>BIND</acronym> 9</title>
<para>
<acronym>BIND</acronym> 9 fully supports all currently
defined forms of IPv6 name to address and address to name
lookups. It will also use IPv6 addresses to make queries when
running on an IPv6 capable system.
</para>
<para>
For forward lookups, <acronym>BIND</acronym> 9 supports
only AAAA records. RFC 3363 deprecated the use of A6 records,
and client-side support for A6 records was accordingly removed
from <acronym>BIND</acronym> 9.
However, authoritative <acronym>BIND</acronym> 9 name servers still
load zone files containing A6 records correctly, answer queries
for A6 records, and accept zone transfer for a zone containing A6
records.
</para>
<para>
For IPv6 reverse lookups, <acronym>BIND</acronym> 9 supports
the traditional "nibble" format used in the
<emphasis>ip6.arpa</emphasis> domain, as well as the older, deprecated
<emphasis>ip6.int</emphasis> domain.
Older versions of <acronym>BIND</acronym> 9
supported the "binary label" (also known as "bitstring") format,
but support of binary labels has been completely removed per
RFC 3363.
Many applications in <acronym>BIND</acronym> 9 do not understand
the binary label format at all any more, and will return an
error if given.
In particular, an authoritative <acronym>BIND</acronym> 9
name server will not load a zone file containing binary labels.
</para>
<para>
For an overview of the format and structure of IPv6 addresses,
see <xref linkend="ipv6addresses"/>.
</para>
<sect2>
<title>Address Lookups Using AAAA Records</title>
<para>
The IPv6 AAAA record is a parallel to the IPv4 A record,
and, unlike the deprecated A6 record, specifies the entire
IPv6 address in a single record. For example,
</para>
<programlisting>
$ORIGIN example.com.
host 3600 IN AAAA 2001:db8::1
</programlisting>
<para>
Use of IPv4-in-IPv6 mapped addresses is not recommended.
If a host has an IPv4 address, use an A record, not
a AAAA, with <literal>::ffff:192.168.42.1</literal> as
the address.
</para>
</sect2>
<sect2>
<title>Address to Name Lookups Using Nibble Format</title>
<para>
When looking up an address in nibble format, the address
components are simply reversed, just as in IPv4, and
<literal>ip6.arpa.</literal> is appended to the
resulting name.
For example, the following would provide reverse name lookup for
a host with address
<literal>2001:db8::1</literal>.
</para>
<programlisting>
$ORIGIN 0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.ip6.arpa.
1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0 14400 IN PTR (
host.example.com. )
</programlisting>
</sect2>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch05">
<title>The <acronym>BIND</acronym> 9 Lightweight Resolver</title>
<sect1>
<title>The Lightweight Resolver Library</title>
<para>
Traditionally applications have been linked with a stub resolver
library that sends recursive DNS queries to a local caching name
server.
</para>
<para>
IPv6 once introduced new complexity into the resolution process,
such as following A6 chains and DNAME records, and simultaneous
lookup of IPv4 and IPv6 addresses. Though most of the complexity was
then removed, these are hard or impossible
to implement in a traditional stub resolver.
</para>
<para>
<acronym>BIND</acronym> 9 therefore can also provide resolution
services to local clients
using a combination of a lightweight resolver library and a resolver
daemon process running on the local host. These communicate using
a simple UDP-based protocol, the "lightweight resolver protocol"
that is distinct from and simpler than the full DNS protocol.
</para>
</sect1>
<sect1 id="lwresd">
<title>Running a Resolver Daemon</title>
<para>
To use the lightweight resolver interface, the system must
run the resolver daemon <command>lwresd</command> or a
local
name server configured with a <command>lwres</command>
statement.
</para>
<para>
By default, applications using the lightweight resolver library will
make
UDP requests to the IPv4 loopback address (127.0.0.1) on port 921.
The
address can be overridden by <command>lwserver</command>
lines in
<filename>/etc/resolv.conf</filename>.
</para>
<para>
The daemon currently only looks in the DNS, but in the future
it may use other sources such as <filename>/etc/hosts</filename>,
NIS, etc.
</para>
<para>
The <command>lwresd</command> daemon is essentially a
caching-only name server that responds to requests using the
lightweight
resolver protocol rather than the DNS protocol. Because it needs
to run on each host, it is designed to require no or minimal
configuration.
Unless configured otherwise, it uses the name servers listed on
<command>nameserver</command> lines in <filename>/etc/resolv.conf</filename>
as forwarders, but is also capable of doing the resolution
autonomously if
none are specified.
</para>
<para>
The <command>lwresd</command> daemon may also be
configured with a
<filename>named.conf</filename> style configuration file,
in
<filename>/etc/lwresd.conf</filename> by default. A name
server may also
be configured to act as a lightweight resolver daemon using the
<command>lwres</command> statement in <filename>named.conf</filename>.
</para>
<para>
The number of client queries that the <command>lwresd</command>
daemon is able to serve can be set using the
<option>lwres-tasks</option> and <option>lwres-clients</option>
statements in the configuration.
</para>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch06">
<title><acronym>BIND</acronym> 9 Configuration Reference</title>
<para>
<acronym>BIND</acronym> 9 configuration is broadly similar
to <acronym>BIND</acronym> 8; however, there are a few new
areas
of configuration, such as views. <acronym>BIND</acronym>
8 configuration files should work with few alterations in <acronym>BIND</acronym>
9, although more complex configurations should be reviewed to check
if they can be more efficiently implemented using the new features
found in <acronym>BIND</acronym> 9.
</para>
<para>
<acronym>BIND</acronym> 4 configuration files can be
converted to the new format
using the shell script
<filename>contrib/named-bootconf/named-bootconf.sh</filename>.
</para>
<sect1 id="configuration_file_elements">
<title>Configuration File Elements</title>
<para>
Following is a list of elements used throughout the <acronym>BIND</acronym> configuration
file documentation:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.855in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.770in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<varname>acl_name</varname>
</para>
</entry>
<entry colname="2">
<para>
The name of an <varname>address_match_list</varname> as
defined by the <command>acl</command> statement.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>address_match_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of one or more
<varname>ip_addr</varname>,
<varname>ip_prefix</varname>, <varname>key_id</varname>,
or <varname>acl_name</varname> elements, see
<xref linkend="address_match_lists"/>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>masters_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A named list of one or more <varname>ip_addr</varname>
with optional <varname>key_id</varname> and/or
<varname>ip_port</varname>.
A <varname>masters_list</varname> may include other
<varname>masters_lists</varname>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>domain_name</varname>
</para>
</entry>
<entry colname="2">
<para>
A quoted string which will be used as
a DNS name, for example "<literal>my.test.domain</literal>".
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>namelist</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of one or more <varname>domain_name</varname>
elements.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>dotted_decimal</varname>
</para>
</entry>
<entry colname="2">
<para>
One to four integers valued 0 through
255 separated by dots (`.'), such as <command>123</command>,
<command>45.67</command> or <command>89.123.45.67</command>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip4_addr</varname>
</para>
</entry>
<entry colname="2">
<para>
An IPv4 address with exactly four elements
in <varname>dotted_decimal</varname> notation.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip6_addr</varname>
</para>
</entry>
<entry colname="2">
<para>
An IPv6 address, such as <command>2001:db8::1234</command>.
IPv6 scoped addresses that have ambiguity on their
scope zones must be disambiguated by an appropriate
zone ID with the percent character (`%') as
delimiter. It is strongly recommended to use
string zone names rather than numeric identifiers,
in order to be robust against system configuration
changes. However, since there is no standard
mapping for such names and identifier values,
currently only interface names as link identifiers
are supported, assuming one-to-one mapping between
interfaces and links. For example, a link-local
address <command>fe80::1</command> on the link
attached to the interface <command>ne0</command>
can be specified as <command>fe80::1%ne0</command>.
Note that on most systems link-local addresses
always have the ambiguity, and need to be
disambiguated.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_addr</varname>
</para>
</entry>
<entry colname="2">
<para>
An <varname>ip4_addr</varname> or <varname>ip6_addr</varname>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_port</varname>
</para>
</entry>
<entry colname="2">
<para>
An IP port <varname>number</varname>.
The <varname>number</varname> is limited to 0
through 65535, with values
below 1024 typically restricted to use by processes running
as root.
In some cases, an asterisk (`*') character can be used as a
placeholder to
select a random high-numbered port.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ip_prefix</varname>
</para>
</entry>
<entry colname="2">
<para>
An IP network specified as an <varname>ip_addr</varname>,
followed by a slash (`/') and then the number of bits in the
netmask.
Trailing zeros in a <varname>ip_addr</varname>
may omitted.
For example, <command>127/8</command> is the
network <command>127.0.0.0</command> with
netmask <command>255.0.0.0</command> and <command>1.2.3.0/28</command> is
network <command>1.2.3.0</command> with netmask <command>255.255.255.240</command>.
</para>
<para>
When specifying a prefix involving a IPv6 scoped address
the scope may be omitted. In that case the prefix will
match packets from any scope.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>key_id</varname>
</para>
</entry>
<entry colname="2">
<para>
A <varname>domain_name</varname> representing
the name of a shared key, to be used for transaction
security.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>key_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of one or more
<varname>key_id</varname>s,
separated by semicolons and ending with a semicolon.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>number</varname>
</para>
</entry>
<entry colname="2">
<para>
A non-negative 32-bit integer
(i.e., a number between 0 and 4294967295, inclusive).
Its acceptable value might further
be limited by the context in which it is used.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>path_name</varname>
</para>
</entry>
<entry colname="2">
<para>
A quoted string which will be used as
a pathname, such as <filename>zones/master/my.test.domain</filename>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>port_list</varname>
</para>
</entry>
<entry colname="2">
<para>
A list of an <varname>ip_port</varname> or a port
range.
A port range is specified in the form of
<userinput>range</userinput> followed by
two <varname>ip_port</varname>s,
<varname>port_low</varname> and
<varname>port_high</varname>, which represents
port numbers from <varname>port_low</varname> through
<varname>port_high</varname>, inclusive.
<varname>port_low</varname> must not be larger than
<varname>port_high</varname>.
For example,
<userinput>range 1024 65535</userinput> represents
ports from 1024 through 65535.
In either case an asterisk (`*') character is not
allowed as a valid <varname>ip_port</varname>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>size_spec</varname>
</para>
</entry>
<entry colname="2">
<para>
A number, the word <userinput>unlimited</userinput>,
or the word <userinput>default</userinput>.
</para>
<para>
An <varname>unlimited</varname> <varname>size_spec</varname> requests unlimited
use, or the maximum available amount. A <varname>default size_spec</varname> uses
the limit that was in force when the server was started.
</para>
<para>
A <varname>number</varname> can optionally be
followed by a scaling factor:
<userinput>K</userinput> or <userinput>k</userinput>
for kilobytes,
<userinput>M</userinput> or <userinput>m</userinput>
for megabytes, and
<userinput>G</userinput> or <userinput>g</userinput> for gigabytes,
which scale by 1024, 1024*1024, and 1024*1024*1024
respectively.
</para>
<para>
The value must be representable as a 64-bit unsigned integer
(0 to 18446744073709551615, inclusive).
Using <varname>unlimited</varname> is the best
way
to safely set a really large number.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>yes_or_no</varname>
</para>
</entry>
<entry colname="2">
<para>
Either <userinput>yes</userinput> or <userinput>no</userinput>.
The words <userinput>true</userinput> and <userinput>false</userinput> are
also accepted, as are the numbers <userinput>1</userinput>
and <userinput>0</userinput>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>dialup_option</varname>
</para>
</entry>
<entry colname="2">
<para>
One of <userinput>yes</userinput>,
<userinput>no</userinput>, <userinput>notify</userinput>,
<userinput>notify-passive</userinput>, <userinput>refresh</userinput> or
<userinput>passive</userinput>.
When used in a zone, <userinput>notify-passive</userinput>,
<userinput>refresh</userinput>, and <userinput>passive</userinput>
are restricted to slave and stub zones.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<sect2 id="address_match_lists">
<title>Address Match Lists</title>
<sect3>
<title>Syntax</title>
<programlisting><varname>address_match_list</varname> = address_match_list_element ;
<optional> address_match_list_element; ... </optional>
<varname>address_match_list_element</varname> = <optional> ! </optional> (ip_address <optional>/length</optional> |
key key_id | acl_name | { address_match_list } )
</programlisting>
</sect3>
<sect3>
<title>Definition and Usage</title>
<para>
Address match lists are primarily used to determine access
control for various server operations. They are also used in
the <command>listen-on</command> and <command>sortlist</command>
statements. The elements which constitute an address match
list can be any of the following:
</para>
<itemizedlist>
<listitem>
<simpara>an IP address (IPv4 or IPv6)</simpara>
</listitem>
<listitem>
<simpara>an IP prefix (in `/' notation)</simpara>
</listitem>
<listitem>
<simpara>
a key ID, as defined by the <command>key</command>
statement
</simpara>
</listitem>
<listitem>
<simpara>the name of an address match list defined with
the <command>acl</command> statement
</simpara>
</listitem>
<listitem>
<simpara>a nested address match list enclosed in braces</simpara>
</listitem>
</itemizedlist>
<para>
Elements can be negated with a leading exclamation mark (`!'),
and the match list names "any", "none", "localhost", and
"localnets" are predefined. More information on those names
can be found in the description of the acl statement.
</para>
<para>
The addition of the key clause made the name of this syntactic
element something of a misnomer, since security keys can be used
to validate access without regard to a host or network address.
Nonetheless, the term "address match list" is still used
throughout the documentation.
</para>
<para>
When a given IP address or prefix is compared to an address
match list, the comparison takes place in approximately O(1)
time. However, key comparisons require that the list of keys
be traversed until a matching key is found, and therefore may
be somewhat slower.
</para>
<para>
The interpretation of a match depends on whether the list is being
used for access control, defining <command>listen-on</command> ports, or in a
<command>sortlist</command>, and whether the element was negated.
</para>
<para>
When used as an access control list, a non-negated match
allows access and a negated match denies access. If
there is no match, access is denied. The clauses
<command>allow-notify</command>,
<command>allow-recursion</command>,
<command>allow-recursion-on</command>,
<command>allow-query</command>,
<command>allow-query-on</command>,
<command>allow-query-cache</command>,
<command>allow-query-cache-on</command>,
<command>allow-transfer</command>,
<command>allow-update</command>,
<command>allow-update-forwarding</command>, and
<command>blackhole</command> all use address match
lists. Similarly, the <command>listen-on</command> option will cause the
server to refuse queries on any of the machine's
addresses which do not match the list.
</para>
<para>
Order of insertion is significant. If more than one element
in an ACL is found to match a given IP address or prefix,
preference will be given to the one that came
<emphasis>first</emphasis> in the ACL definition.
Because of this first-match behavior, an element that
defines a subset of another element in the list should
come before the broader element, regardless of whether
either is negated. For example, in
<command>1.2.3/24; ! 1.2.3.13;</command>
the 1.2.3.13 element is completely useless because the
algorithm will match any lookup for 1.2.3.13 to the 1.2.3/24
element. Using <command>! 1.2.3.13; 1.2.3/24</command> fixes
that problem by having 1.2.3.13 blocked by the negation, but
all other 1.2.3.* hosts fall through.
</para>
</sect3>
</sect2>
<sect2>
<title>Comment Syntax</title>
<para>
The <acronym>BIND</acronym> 9 comment syntax allows for
comments to appear
anywhere that whitespace may appear in a <acronym>BIND</acronym> configuration
file. To appeal to programmers of all kinds, they can be written
in the C, C++, or shell/perl style.
</para>
<sect3>
<title>Syntax</title>
<para>
<programlisting>/* This is a <acronym>BIND</acronym> comment as in C */</programlisting>
<programlisting>// This is a <acronym>BIND</acronym> comment as in C++</programlisting>
<programlisting># This is a <acronym>BIND</acronym> comment as in common UNIX shells
# and perl</programlisting>
</para>
</sect3>
<sect3>
<title>Definition and Usage</title>
<para>
Comments may appear anywhere that whitespace may appear in
a <acronym>BIND</acronym> configuration file.
</para>
<para>
C-style comments start with the two characters /* (slash,
star) and end with */ (star, slash). Because they are completely
delimited with these characters, they can be used to comment only
a portion of a line or to span multiple lines.
</para>
<para>
C-style comments cannot be nested. For example, the following
is not valid because the entire comment ends with the first */:
</para>
<para>
<programlisting>/* This is the start of a comment.
This is still part of the comment.
/* This is an incorrect attempt at nesting a comment. */
This is no longer in any comment. */
</programlisting>
</para>
<para>
C++-style comments start with the two characters // (slash,
slash) and continue to the end of the physical line. They cannot
be continued across multiple physical lines; to have one logical
comment span multiple lines, each line must use the // pair.
For example:
</para>
<para>
<programlisting>// This is the start of a comment. The next line
// is a new comment, even though it is logically
// part of the previous comment.
</programlisting>
</para>
<para>
Shell-style (or perl-style, if you prefer) comments start
with the character <literal>#</literal> (number sign)
and continue to the end of the
physical line, as in C++ comments.
For example:
</para>
<para>
<programlisting># This is the start of a comment. The next line
# is a new comment, even though it is logically
# part of the previous comment.
</programlisting>
</para>
<warning>
<para>
You cannot use the semicolon (`;') character
to start a comment such as you would in a zone file. The
semicolon indicates the end of a configuration
statement.
</para>
</warning>
</sect3>
</sect2>
</sect1>
<sect1 id="Configuration_File_Grammar">
<title>Configuration File Grammar</title>
<para>
A <acronym>BIND</acronym> 9 configuration consists of
statements and comments.
Statements end with a semicolon. Statements and comments are the
only elements that can appear without enclosing braces. Many
statements contain a block of sub-statements, which are also
terminated with a semicolon.
</para>
<para>
The following statements are supported:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="2Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.336in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.778in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>acl</command></para>
</entry>
<entry colname="2">
<para>
defines a named IP address
matching list, for access control and other uses.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>controls</command></para>
</entry>
<entry colname="2">
<para>
declares control channels to be used
by the <command>rndc</command> utility.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>include</command></para>
</entry>
<entry colname="2">
<para>
includes a file.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>key</command></para>
</entry>
<entry colname="2">
<para>
specifies key information for use in
authentication and authorization using TSIG.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>logging</command></para>
</entry>
<entry colname="2">
<para>
specifies what the server logs, and where
the log messages are sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>lwres</command></para>
</entry>
<entry colname="2">
<para>
configures <command>named</command> to
also act as a light-weight resolver daemon (<command>lwresd</command>).
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>masters</command></para>
</entry>
<entry colname="2">
<para>
defines a named masters list for
inclusion in stub and slave zone masters clauses.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>options</command></para>
</entry>
<entry colname="2">
<para>
controls global server configuration
options and sets defaults for other statements.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>server</command></para>
</entry>
<entry colname="2">
<para>
sets certain configuration options on
a per-server basis.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>statistics-channels</command></para>
</entry>
<entry colname="2">
<para>
declares communication channels to get access to
<command>named</command> statistics.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>trusted-keys</command></para>
</entry>
<entry colname="2">
<para>
defines trusted DNSSEC keys.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>managed-keys</command></para>
</entry>
<entry colname="2">
<para>
lists DNSSEC keys to be kept up to date
using RFC 5011 trust anchor maintenance.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>view</command></para>
</entry>
<entry colname="2">
<para>
defines a view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>zone</command></para>
</entry>
<entry colname="2">
<para>
defines a zone.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The <command>logging</command> and
<command>options</command> statements may only occur once
per
configuration.
</para>
<sect2>
<title><command>acl</command> Statement Grammar</title>
<programlisting><command>acl</command> acl-name {
address_match_list
};
</programlisting>
</sect2>
<sect2 id="acl">
<title><command>acl</command> Statement Definition and
Usage</title>
<para>
The <command>acl</command> statement assigns a symbolic
name to an address match list. It gets its name from a primary
use of address match lists: Access Control Lists (ACLs).
</para>
<para>
Note that an address match list's name must be defined
with <command>acl</command> before it can be used
elsewhere; no forward references are allowed.
</para>
<para>
The following ACLs are built-in:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.130in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>any</command></para>
</entry>
<entry colname="2">
<para>
Matches all hosts.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>none</command></para>
</entry>
<entry colname="2">
<para>
Matches no hosts.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>localhost</command></para>
</entry>
<entry colname="2">
<para>
Matches the IPv4 and IPv6 addresses of all network
interfaces on the system.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>localnets</command></para>
</entry>
<entry colname="2">
<para>
Matches any host on an IPv4 or IPv6 network
for which the system has an interface.
Some systems do not provide a way to determine the prefix
lengths of
local IPv6 addresses.
In such a case, <command>localnets</command>
only matches the local
IPv6 addresses, just like <command>localhost</command>.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect2>
<sect2>
<title><command>controls</command> Statement Grammar</title>
<programlisting><command>controls</command> {
[ inet ( ip_addr | * ) [ port ip_port ]
allow { <replaceable> address_match_list </replaceable> }
keys { <replaceable>key_list</replaceable> }; ]
[ inet ...; ]
[ unix <replaceable>path</replaceable> perm <replaceable>number</replaceable> owner <replaceable>number</replaceable> group <replaceable>number</replaceable>
keys { <replaceable>key_list</replaceable> }; ]
[ unix ...; ]
};
</programlisting>
</sect2>
<sect2 id="controls_statement_definition_and_usage">
<title><command>controls</command> Statement Definition and
Usage</title>
<para>
The <command>controls</command> statement declares control
channels to be used by system administrators to control the
operation of the name server. These control channels are
used by the <command>rndc</command> utility to send
commands to and retrieve non-DNS results from a name server.
</para>
<para>
An <command>inet</command> control channel is a TCP socket
listening at the specified <command>ip_port</command> on the
specified <command>ip_addr</command>, which can be an IPv4 or IPv6
address. An <command>ip_addr</command> of <literal>*</literal> (asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an <command>ip_addr</command> of <literal>::</literal>.
If you will only use <command>rndc</command> on the local host,
using the loopback address (<literal>127.0.0.1</literal>
or <literal>::1</literal>) is recommended for maximum security.
</para>
<para>
If no port is specified, port 953 is used. The asterisk
"<literal>*</literal>" cannot be used for <command>ip_port</command>.
</para>
<para>
The ability to issue commands over the control channel is
restricted by the <command>allow</command> and
<command>keys</command> clauses.
Connections to the control channel are permitted based on the
<command>address_match_list</command>. This is for simple
IP address based filtering only; any <command>key_id</command>
elements of the <command>address_match_list</command>
are ignored.
</para>
<para>
A <command>unix</command> control channel is a UNIX domain
socket listening at the specified path in the file system.
Access to the socket is specified by the <command>perm</command>,
<command>owner</command> and <command>group</command> clauses.
Note on some platforms (SunOS and Solaris) the permissions
(<command>perm</command>) are applied to the parent directory
as the permissions on the socket itself are ignored.
</para>
<para>
The primary authorization mechanism of the command
channel is the <command>key_list</command>, which
contains a list of <command>key_id</command>s.
Each <command>key_id</command> in the <command>key_list</command>
is authorized to execute commands over the control channel.
See <xref linkend="rndc"/> in <xref linkend="admin_tools"/>)
for information about configuring keys in <command>rndc</command>.
</para>
<para>
If no <command>controls</command> statement is present,
<command>named</command> will set up a default
control channel listening on the loopback address 127.0.0.1
and its IPv6 counterpart ::1.
In this case, and also when the <command>controls</command> statement
is present but does not have a <command>keys</command> clause,
<command>named</command> will attempt to load the command channel key
from the file <filename>rndc.key</filename> in
<filename>/etc</filename> (or whatever <varname>sysconfdir</varname>
was specified as when <acronym>BIND</acronym> was built).
To create a <filename>rndc.key</filename> file, run
<userinput>rndc-confgen -a</userinput>.
</para>
<para>
The <filename>rndc.key</filename> feature was created to
ease the transition of systems from <acronym>BIND</acronym> 8,
which did not have digital signatures on its command channel
messages and thus did not have a <command>keys</command> clause.
It makes it possible to use an existing <acronym>BIND</acronym> 8
configuration file in <acronym>BIND</acronym> 9 unchanged,
and still have <command>rndc</command> work the same way
<command>ndc</command> worked in BIND 8, simply by executing the
command <userinput>rndc-confgen -a</userinput> after BIND 9 is
installed.
</para>
<para>
Since the <filename>rndc.key</filename> feature
is only intended to allow the backward-compatible usage of
<acronym>BIND</acronym> 8 configuration files, this
feature does not
have a high degree of configurability. You cannot easily change
the key name or the size of the secret, so you should make a
<filename>rndc.conf</filename> with your own key if you
wish to change
those things. The <filename>rndc.key</filename> file
also has its
permissions set such that only the owner of the file (the user that
<command>named</command> is running as) can access it.
If you
desire greater flexibility in allowing other users to access
<command>rndc</command> commands, then you need to create
a
<filename>rndc.conf</filename> file and make it group
readable by a group
that contains the users who should have access.
</para>
<para>
To disable the command channel, use an empty
<command>controls</command> statement:
<command>controls { };</command>.
</para>
</sect2>
<sect2>
<title><command>include</command> Statement Grammar</title>
<programlisting><command>include</command> <replaceable>filename</replaceable>;</programlisting>
</sect2>
<sect2>
<title><command>include</command> Statement Definition and
Usage</title>
<para>
The <command>include</command> statement inserts the
specified file at the point where the <command>include</command>
statement is encountered. The <command>include</command>
statement facilitates the administration of configuration
files
by permitting the reading or writing of some things but not
others. For example, the statement could include private keys
that are readable only by the name server.
</para>
</sect2>
<sect2>
<title><command>key</command> Statement Grammar</title>
<programlisting><command>key</command> <replaceable>key_id</replaceable> {
algorithm <replaceable>string</replaceable>;
secret <replaceable>string</replaceable>;
};
</programlisting>
</sect2>
<sect2>
<title><command>key</command> Statement Definition and Usage</title>
<para>
The <command>key</command> statement defines a shared
secret key for use with TSIG (see <xref linkend="tsig"/>)
or the command channel
(see <xref linkend="controls_statement_definition_and_usage"/>).
</para>
<para>
The <command>key</command> statement can occur at the
top level
of the configuration file or inside a <command>view</command>
statement. Keys defined in top-level <command>key</command>
statements can be used in all views. Keys intended for use in
a <command>controls</command> statement
(see <xref linkend="controls_statement_definition_and_usage"/>)
must be defined at the top level.
</para>
<para>
The <replaceable>key_id</replaceable>, also known as the
key name, is a domain name uniquely identifying the key. It can
be used in a <command>server</command>
statement to cause requests sent to that
server to be signed with this key, or in address match lists to
verify that incoming requests have been signed with a key
matching this name, algorithm, and secret.
</para>
<para>
The <replaceable>algorithm_id</replaceable> is a string
that specifies a security/authentication algorithm. Named
supports <literal>hmac-md5</literal>,
<literal>hmac-sha1</literal>, <literal>hmac-sha224</literal>,
<literal>hmac-sha256</literal>, <literal>hmac-sha384</literal>
and <literal>hmac-sha512</literal> TSIG authentication.
Truncated hashes are supported by appending the minimum
number of required bits preceded by a dash, e.g.
<literal>hmac-sha1-80</literal>. The
<replaceable>secret_string</replaceable> is the secret
to be used by the algorithm, and is treated as a base-64
encoded string.
</para>
</sect2>
<sect2>
<title><command>logging</command> Statement Grammar</title>
<programlisting><command>logging</command> {
[ <command>channel</command> <replaceable>channel_name</replaceable> {
( <command>file</command> <replaceable>path_name</replaceable>
[ <command>versions</command> ( <replaceable>number</replaceable> | <command>unlimited</command> ) ]
[ <command>size</command> <replaceable>size spec</replaceable> ]
| <command>syslog</command> <replaceable>syslog_facility</replaceable>
| <command>stderr</command>
| <command>null</command> );
[ <command>severity</command> (<option>critical</option> | <option>error</option> | <option>warning</option> | <option>notice</option> |
<option>info</option> | <option>debug</option> [ <replaceable>level</replaceable> ] | <option>dynamic</option> ); ]
[ <command>print-category</command> <option>yes</option> or <option>no</option>; ]
[ <command>print-severity</command> <option>yes</option> or <option>no</option>; ]
[ <command>print-time</command> <option>yes</option> or <option>no</option>; ]
}; ]
[ <command>category</command> <replaceable>category_name</replaceable> {
<replaceable>channel_name</replaceable> ; [ <replaceable>channel_name</replaceable> ; ... ]
}; ]
...
};
</programlisting>
</sect2>
<sect2>
<title><command>logging</command> Statement Definition and
Usage</title>
<para>
The <command>logging</command> statement configures a
wide
variety of logging options for the name server. Its <command>channel</command> phrase
associates output methods, format options and severity levels with
a name that can then be used with the <command>category</command> phrase
to select how various classes of messages are logged.
</para>
<para>
Only one <command>logging</command> statement is used to
define
as many channels and categories as are wanted. If there is no <command>logging</command> statement,
the logging configuration will be:
</para>
<programlisting>logging {
category default { default_syslog; default_debug; };
category unmatched { null; };
};
</programlisting>
<para>
In <acronym>BIND</acronym> 9, the logging configuration
is only established when
the entire configuration file has been parsed. In <acronym>BIND</acronym> 8, it was
established as soon as the <command>logging</command>
statement
was parsed. When the server is starting up, all logging messages
regarding syntax errors in the configuration file go to the default
channels, or to standard error if the "<option>-g</option>" option
was specified.
</para>
<sect3>
<title>The <command>channel</command> Phrase</title>
<para>
All log output goes to one or more <emphasis>channels</emphasis>;
you can make as many of them as you want.
</para>
<para>
Every channel definition must include a destination clause that
says whether messages selected for the channel go to a file, to a
particular syslog facility, to the standard error stream, or are
discarded. It can optionally also limit the message severity level
that will be accepted by the channel (the default is
<command>info</command>), and whether to include a
<command>named</command>-generated time stamp, the
category name
and/or severity level (the default is not to include any).
</para>
<para>
The <command>null</command> destination clause
causes all messages sent to the channel to be discarded;
in that case, other options for the channel are meaningless.
</para>
<para>
The <command>file</command> destination clause directs
the channel
to a disk file. It can include limitations
both on how large the file is allowed to become, and how many
versions
of the file will be saved each time the file is opened.
</para>
<para>
If you use the <command>versions</command> log file
option, then
<command>named</command> will retain that many backup
versions of the file by
renaming them when opening. For example, if you choose to keep
three old versions
of the file <filename>lamers.log</filename>, then just
before it is opened
<filename>lamers.log.1</filename> is renamed to
<filename>lamers.log.2</filename>, <filename>lamers.log.0</filename> is renamed
to <filename>lamers.log.1</filename>, and <filename>lamers.log</filename> is
renamed to <filename>lamers.log.0</filename>.
You can say <command>versions unlimited</command> to
not limit
the number of versions.
If a <command>size</command> option is associated with
the log file,
then renaming is only done when the file being opened exceeds the
indicated size. No backup versions are kept by default; any
existing
log file is simply appended.
</para>
<para>
The <command>size</command> option for files is used
to limit log
growth. If the file ever exceeds the size, then <command>named</command> will
stop writing to the file unless it has a <command>versions</command> option
associated with it. If backup versions are kept, the files are
rolled as
described above and a new one begun. If there is no
<command>versions</command> option, no more data will
be written to the log
until some out-of-band mechanism removes or truncates the log to
less than the
maximum size. The default behavior is not to limit the size of
the
file.
</para>
<para>
Example usage of the <command>size</command> and
<command>versions</command> options:
</para>
<programlisting>channel an_example_channel {
file "example.log" versions 3 size 20m;
print-time yes;
print-category yes;
};
</programlisting>
<para>
The <command>syslog</command> destination clause
directs the
channel to the system log. Its argument is a
syslog facility as described in the <command>syslog</command> man
page. Known facilities are <command>kern</command>, <command>user</command>,
<command>mail</command>, <command>daemon</command>, <command>auth</command>,
<command>syslog</command>, <command>lpr</command>, <command>news</command>,
<command>uucp</command>, <command>cron</command>, <command>authpriv</command>,
<command>ftp</command>, <command>local0</command>, <command>local1</command>,
<command>local2</command>, <command>local3</command>, <command>local4</command>,
<command>local5</command>, <command>local6</command> and
<command>local7</command>, however not all facilities
are supported on
all operating systems.
How <command>syslog</command> will handle messages
sent to
this facility is described in the <command>syslog.conf</command> man
page. If you have a system which uses a very old version of <command>syslog</command> that
only uses two arguments to the <command>openlog()</command> function,
then this clause is silently ignored.
</para>
<para>
The <command>severity</command> clause works like <command>syslog</command>'s
"priorities", except that they can also be used if you are writing
straight to a file rather than using <command>syslog</command>.
Messages which are not at least of the severity level given will
not be selected for the channel; messages of higher severity
levels
will be accepted.
</para>
<para>
If you are using <command>syslog</command>, then the <command>syslog.conf</command> priorities
will also determine what eventually passes through. For example,
defining a channel facility and severity as <command>daemon</command> and <command>debug</command> but
only logging <command>daemon.warning</command> via <command>syslog.conf</command> will
cause messages of severity <command>info</command> and
<command>notice</command> to
be dropped. If the situation were reversed, with <command>named</command> writing
messages of only <command>warning</command> or higher,
then <command>syslogd</command> would
print all messages it received from the channel.
</para>
<para>
The <command>stderr</command> destination clause
directs the
channel to the server's standard error stream. This is intended
for
use when the server is running as a foreground process, for
example
when debugging a configuration.
</para>
<para>
The server can supply extensive debugging information when
it is in debugging mode. If the server's global debug level is
greater
than zero, then debugging mode will be active. The global debug
level is set either by starting the <command>named</command> server
with the <option>-d</option> flag followed by a positive integer,
or by running <command>rndc trace</command>.
The global debug level
can be set to zero, and debugging mode turned off, by running <command>rndc
notrace</command>. All debugging messages in the server have a debug
level, and higher debug levels give more detailed output. Channels
that specify a specific debug severity, for example:
</para>
<programlisting>channel specific_debug_level {
file "foo";
severity debug 3;
};
</programlisting>
<para>
will get debugging output of level 3 or less any time the
server is in debugging mode, regardless of the global debugging
level. Channels with <command>dynamic</command>
severity use the
server's global debug level to determine what messages to print.
</para>
<para>
If <command>print-time</command> has been turned on,
then
the date and time will be logged. <command>print-time</command> may
be specified for a <command>syslog</command> channel,
but is usually
pointless since <command>syslog</command> also logs
the date and
time. If <command>print-category</command> is
requested, then the
category of the message will be logged as well. Finally, if <command>print-severity</command> is
on, then the severity level of the message will be logged. The <command>print-</command> options may
be used in any combination, and will always be printed in the
following
order: time, category, severity. Here is an example where all
three <command>print-</command> options
are on:
</para>
<para>
<computeroutput>28-Feb-2000 15:05:32.863 general: notice: running</computeroutput>
</para>
<para>
There are four predefined channels that are used for
<command>named</command>'s default logging as follows.
How they are
used is described in <xref linkend="the_category_phrase"/>.
</para>
<programlisting>channel default_syslog {
// send to syslog's daemon facility
syslog daemon;
// only send priority info and higher
severity info;
channel default_debug {
// write to named.run in the working directory
// Note: stderr is used instead of "named.run" if
// the server is started with the '-f' option.
file "named.run";
// log at the server's current debug level
severity dynamic;
};
channel default_stderr {
// writes to stderr
stderr;
// only send priority info and higher
severity info;
};
channel null {
// toss anything sent to this channel
null;
};
</programlisting>
<para>
The <command>default_debug</command> channel has the
special
property that it only produces output when the server's debug
level is
nonzero. It normally writes to a file called <filename>named.run</filename>
in the server's working directory.
</para>
<para>
For security reasons, when the "<option>-u</option>"
command line option is used, the <filename>named.run</filename> file
is created only after <command>named</command> has
changed to the
new UID, and any debug output generated while <command>named</command> is
starting up and still running as root is discarded. If you need
to capture this output, you must run the server with the "<option>-g</option>"
option and redirect standard error to a file.
</para>
<para>
Once a channel is defined, it cannot be redefined. Thus you
cannot alter the built-in channels directly, but you can modify
the default logging by pointing categories at channels you have
defined.
</para>
</sect3>
<sect3 id="the_category_phrase">
<title>The <command>category</command> Phrase</title>
<para>
There are many categories, so you can send the logs you want
to see wherever you want, without seeing logs you don't want. If
you don't specify a list of channels for a category, then log
messages
in that category will be sent to the <command>default</command> category
instead. If you don't specify a default category, the following
"default default" is used:
</para>
<programlisting>category default { default_syslog; default_debug; };
</programlisting>
<para>
As an example, let's say you want to log security events to
a file, but you also want keep the default logging behavior. You'd
specify the following:
</para>
<programlisting>channel my_security_channel {
file "my_security_file";
severity info;
};
category security {
my_security_channel;
default_syslog;
default_debug;
};</programlisting>
<para>
To discard all messages in a category, specify the <command>null</command> channel:
</para>
<programlisting>category xfer-out { null; };
category notify { null; };
</programlisting>
<para>
Following are the available categories and brief descriptions
of the types of log information they contain. More
categories may be added in future <acronym>BIND</acronym> releases.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>default</command></para>
</entry>
<entry colname="2">
<para>
The default category defines the logging
options for those categories where no specific
configuration has been
defined.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>general</command></para>
</entry>
<entry colname="2">
<para>
The catch-all. Many things still aren't
classified into categories, and they all end up here.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>database</command></para>
</entry>
<entry colname="2">
<para>
Messages relating to the databases used
internally by the name server to store zone and cache
data.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>security</command></para>
</entry>
<entry colname="2">
<para>
Approval and denial of requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>config</command></para>
</entry>
<entry colname="2">
<para>
Configuration file parsing and processing.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>resolver</command></para>
</entry>
<entry colname="2">
<para>
DNS resolution, such as the recursive
lookups performed on behalf of clients by a caching name
server.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>xfer-in</command></para>
</entry>
<entry colname="2">
<para>
Zone transfers the server is receiving.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>xfer-out</command></para>
</entry>
<entry colname="2">
<para>
Zone transfers the server is sending.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>notify</command></para>
</entry>
<entry colname="2">
<para>
The NOTIFY protocol.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>client</command></para>
</entry>
<entry colname="2">
<para>
Processing of client requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>unmatched</command></para>
</entry>
<entry colname="2">
<para>
Messages that <command>named</command> was unable to determine the
class of or for which there was no matching <command>view</command>.
A one line summary is also logged to the <command>client</command> category.
This category is best sent to a file or stderr, by
default it is sent to
the <command>null</command> channel.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>network</command></para>
</entry>
<entry colname="2">
<para>
Network operations.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>update</command></para>
</entry>
<entry colname="2">
<para>
Dynamic updates.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>update-security</command></para>
</entry>
<entry colname="2">
<para>
Approval and denial of update requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>queries</command></para>
</entry>
<entry colname="2">
<para>
Specify where queries should be logged to.
</para>
<para>
At startup, specifying the category <command>queries</command> will also
enable query logging unless <command>querylog</command> option has been
specified.
</para>
<para>
The query log entry reports the client's IP
address and port number, and the query name,
class and type. Next it reports whether the
Recursion Desired flag was set (+ if set, -
if not set), if the query was signed (S),
EDNS was in use (E), if TCP was used (T), if
DO (DNSSEC Ok) was set (D), or if CD (Checking
Disabled) was set (C). After this the
destination address the query was sent to is
reported.
</para>
<para>
<computeroutput>client 127.0.0.1#62536: query: www.example.com IN AAAA +SE</computeroutput>
</para>
<para>
<computeroutput>client ::1#62537: query: www.example.net IN AAAA -SE</computeroutput>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>query-errors</command></para>
</entry>
<entry colname="2">
<para>
Information about queries that resulted in some
failure.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>dispatch</command></para>
</entry>
<entry colname="2">
<para>
Dispatching of incoming packets to the
server modules where they are to be processed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>dnssec</command></para>
</entry>
<entry colname="2">
<para>
DNSSEC and TSIG protocol processing.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>lame-servers</command></para>
</entry>
<entry colname="2">
<para>
Lame servers. These are misconfigurations
in remote servers, discovered by BIND 9 when trying to
query those servers during resolution.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>delegation-only</command></para>
</entry>
<entry colname="2">
<para>
Delegation only. Logs queries that have been
forced to NXDOMAIN as the result of a
delegation-only zone or a
<command>delegation-only</command> in a hint
or stub zone declaration.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>edns-disabled</command></para>
</entry>
<entry colname="2">
<para>
Log queries that have been forced to use plain
DNS due to timeouts. This is often due to
the remote servers not being RFC 1034 compliant
(not always returning FORMERR or similar to
EDNS queries and other extensions to the DNS
when they are not understood). In other words, this is
targeted at servers that fail to respond to
DNS queries that they don't understand.
</para>
<para>
Note: the log message can also be due to
packet loss. Before reporting servers for
non-RFC 1034 compliance they should be re-tested
to determine the nature of the non-compliance.
This testing should prevent or reduce the
number of false-positive reports.
</para>
<para>
Note: eventually <command>named</command> will have to stop
treating such timeouts as due to RFC 1034 non
compliance and start treating it as plain
packet loss. Falsely classifying packet
loss as due to RFC 1034 non compliance impacts
on DNSSEC validation which requires EDNS for
the DNSSEC records to be returned.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RPZ</command></para>
</entry>
<entry colname="2">
<para>
Information about errors in response policy zone files,
rewritten responses, and at the highest
<command>debug</command> levels, mere rewriting
attempts.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>The <command>query-errors</command> Category</title>
<para>
The <command>query-errors</command> category is
specifically intended for debugging purposes: To identify
why and how specific queries result in responses which
indicate an error.
Messages of this category are therefore only logged
with <command>debug</command> levels.
</para>
<para>
At the debug levels of 1 or higher, each response with the
rcode of SERVFAIL is logged as follows:
</para>
<para>
<computeroutput>client 127.0.0.1#61502: query failed (SERVFAIL) for www.example.com/IN/AAAA at query.c:3880</computeroutput>
</para>
<para>
This means an error resulting in SERVFAIL was
detected at line 3880 of source file
<filename>query.c</filename>.
Log messages of this level will particularly
help identify the cause of SERVFAIL for an
authoritative server.
</para>
<para>
At the debug levels of 2 or higher, detailed context
information of recursive resolutions that resulted in
SERVFAIL is logged.
The log message will look like as follows:
</para>
<para>
<!-- NOTE: newlines and some spaces added so this would fit on page -->
<programlisting>
fetch completed at resolver.c:2970 for www.example.com/A
in 30.000183: timed out/success [domain:example.com,
referral:2,restart:7,qrysent:8,timeout:5,lame:0,neterr:0,
badresp:1,adberr:0,findfail:0,valfail:0]
</programlisting>
</para>
<para>
The first part before the colon shows that a recursive
resolution for AAAA records of www.example.com completed
in 30.000183 seconds and the final result that led to the
SERVFAIL was determined at line 2970 of source file
<filename>resolver.c</filename>.
</para>
<para>
The following part shows the detected final result and the
latest result of DNSSEC validation.
The latter is always success when no validation attempt
is made.
In this example, this query resulted in SERVFAIL probably
because all name servers are down or unreachable, leading
to a timeout in 30 seconds.
DNSSEC validation was probably not attempted.
</para>
<para>
The last part enclosed in square brackets shows statistics
information collected for this particular resolution
attempt.
The <varname>domain</varname> field shows the deepest zone
that the resolver reached;
it is the zone where the error was finally detected.
The meaning of the other fields is summarized in the
following table.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><varname>referral</varname></para>
</entry>
<entry colname="2">
<para>
The number of referrals the resolver received
throughout the resolution process.
In the above example this is 2, which are most
likely com and example.com.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>restart</varname></para>
</entry>
<entry colname="2">
<para>
The number of cycles that the resolver tried
remote servers at the <varname>domain</varname>
zone.
In each cycle the resolver sends one query
(possibly resending it, depending on the response)
to each known name server of
the <varname>domain</varname> zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>qrysent</varname></para>
</entry>
<entry colname="2">
<para>
The number of queries the resolver sent at the
<varname>domain</varname> zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>timeout</varname></para>
</entry>
<entry colname="2">
<para>
The number of timeouts since the resolver
received the last response.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>lame</varname></para>
</entry>
<entry colname="2">
<para>
The number of lame servers the resolver detected
at the <varname>domain</varname> zone.
A server is detected to be lame either by an
invalid response or as a result of lookup in
BIND9's address database (ADB), where lame
servers are cached.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>neterr</varname></para>
</entry>
<entry colname="2">
<para>
The number of erroneous results that the
resolver encountered in sending queries
at the <varname>domain</varname> zone.
One common case is the remote server is
unreachable and the resolver receives an ICMP
unreachable error message.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>badresp</varname></para>
</entry>
<entry colname="2">
<para>
The number of unexpected responses (other than
<varname>lame</varname>) to queries sent by the
resolver at the <varname>domain</varname> zone.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>adberr</varname></para>
</entry>
<entry colname="2">
<para>
Failures in finding remote server addresses
of the <varname>domain</varname> zone in the ADB.
One common case of this is that the remote
server's name does not have any address records.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>findfail</varname></para>
</entry>
<entry colname="2">
<para>
Failures of resolving remote server addresses.
This is a total number of failures throughout
the resolution process.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><varname>valfail</varname></para>
</entry>
<entry colname="2">
<para>
Failures of DNSSEC validation.
Validation failures are counted throughout
the resolution process (not limited to
the <varname>domain</varname> zone), but should
only happen in <varname>domain</varname>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>rate-limit</command></para>
</entry>
<entry colname="2">
<para>
The start, periodic, and final notices of the
rate limiting of a stream of responses are logged at
<command>info</command> severity in this category.
These messages include a hash value of the domain name
of the response and the name itself,
except when there is insufficient memory to record
the name for the final notice
The final notice is normally delayed until about one
minute after rate limit stops.
A lack of memory can hurry the final notice,
in which case it starts with an asterisk (*).
Various internal events are logged at debug 1 level
and higher.
</para>
<para>
Rate limiting of individual requests
is logged in the <command>queries</command> category
and can be controlled with the
<command>querylog</command> option.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
At the debug levels of 3 or higher, the same messages
as those at the debug 1 level are logged for other errors
than SERVFAIL.
Note that negative responses such as NXDOMAIN are not
regarded as errors here.
</para>
<para>
At the debug levels of 4 or higher, the same messages
as those at the debug 2 level are logged for other errors
than SERVFAIL.
Unlike the above case of level 3, messages are logged for
negative responses.
This is because any unexpected results can be difficult to
debug in the recursion case.
</para>
</sect3>
</sect2>
<sect2>
<title><command>lwres</command> Statement Grammar</title>
<para>
This is the grammar of the <command>lwres</command>
statement in the <filename>named.conf</filename> file:
</para>
<programlisting><command>lwres</command> {
<optional> listen-on { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ;
<optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> view <replaceable>view_name</replaceable>; </optional>
<optional> search { <replaceable>domain_name</replaceable> ; <optional> <replaceable>domain_name</replaceable> ; ... </optional> }; </optional>
<optional> ndots <replaceable>number</replaceable>; </optional>
<optional> lwres-tasks <replaceable>number</replaceable>; </optional>
<optional> lwres-clients <replaceable>number</replaceable>; </optional>
};
</programlisting>
</sect2>
<sect2>
<title><command>lwres</command> Statement Definition and Usage</title>
<para>
The <command>lwres</command> statement configures the
name
server to also act as a lightweight resolver server. (See
<xref linkend="lwresd"/>.) There may be multiple
<command>lwres</command> statements configuring
lightweight resolver servers with different properties.
</para>
<para>
The <command>listen-on</command> statement specifies a
list of
addresses (and ports) that this instance of a lightweight resolver
daemon
should accept requests on. If no port is specified, port 921 is
used.
If this statement is omitted, requests will be accepted on
127.0.0.1,
port 921.
</para>
<para>
The <command>view</command> statement binds this
instance of a
lightweight resolver daemon to a view in the DNS namespace, so that
the
response will be constructed in the same manner as a normal DNS
query
matching this view. If this statement is omitted, the default view
is
used, and if there is no default view, an error is triggered.
</para>
<para>
The <command>search</command> statement is equivalent to
the
<command>search</command> statement in
<filename>/etc/resolv.conf</filename>. It provides a
list of domains
which are appended to relative names in queries.
</para>
<para>
The <command>ndots</command> statement is equivalent to
the
<command>ndots</command> statement in
<filename>/etc/resolv.conf</filename>. It indicates the
minimum
number of dots in a relative domain name that should result in an
exact match lookup before search path elements are appended.
</para>
<para>
The <option>lwres-tasks</option> statement specifies the number
of worker threads the lightweight resolver will dedicate to serving
clients. By default the number is the same as the number of CPUs on
the system; this can be overridden using the <option>-n</option>
command line option when starting the server.
</para>
<para>
The <option>lwres-clients</option> specifies
the number of client objects per thread the lightweight
resolver should create to serve client queries.
By default, if the lightweight resolver runs as a part
of <command>named</command>, 256 client objects are
created for each task; if it runs as <command>lwresd</command>,
1024 client objects are created for each thread. The maximum
value is 32768; higher values will be silently ignored and
the maximum will be used instead.
Note that setting too high a value may overconsume
system resources.
</para>
<para>
The maximum number of client queries that the lightweight
resolver can handle at any one time equals
<option>lwres-tasks</option> times <option>lwres-clients</option>.
</para>
</sect2>
<sect2>
<title><command>masters</command> Statement Grammar</title>
<programlisting>
<command>masters</command> <replaceable>name</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> { ( <replaceable>masters_list</replaceable> |
<replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> <optional>key <replaceable>key</replaceable></optional> ) ; <optional>...</optional> };
</programlisting>
</sect2>
<sect2>
<title><command>masters</command> Statement Definition and
Usage</title>
<para><command>masters</command>
lists allow for a common set of masters to be easily used by
multiple stub and slave zones.
</para>
</sect2>
<sect2>
<title><command>options</command> Statement Grammar</title>
<para>
This is the grammar of the <command>options</command>
statement in the <filename>named.conf</filename> file:
</para>
<programlisting><command>options</command> {
<optional> attach-cache <replaceable>cache_name</replaceable>; </optional>
<optional> version <replaceable>version_string</replaceable>; </optional>
<optional> hostname <replaceable>hostname_string</replaceable>; </optional>
<optional> server-id <replaceable>server_id_string</replaceable>; </optional>
<optional> directory <replaceable>path_name</replaceable>; </optional>
<optional> key-directory <replaceable>path_name</replaceable>; </optional>
<optional> managed-keys-directory <replaceable>path_name</replaceable>; </optional>
<optional> named-xfer <replaceable>path_name</replaceable>; </optional>
<optional> tkey-gssapi-keytab <replaceable>path_name</replaceable>; </optional>
<optional> tkey-gssapi-credential <replaceable>principal</replaceable>; </optional>
<optional> tkey-domain <replaceable>domainname</replaceable>; </optional>
<optional> tkey-dhkey <replaceable>key_name</replaceable> <replaceable>key_tag</replaceable>; </optional>
<optional> cache-file <replaceable>path_name</replaceable>; </optional>
<optional> dump-file <replaceable>path_name</replaceable>; </optional>
<optional> bindkeys-file <replaceable>path_name</replaceable>; </optional>
<optional> secroots-file <replaceable>path_name</replaceable>; </optional>
<optional> session-keyfile <replaceable>path_name</replaceable>; </optional>
<optional> session-keyname <replaceable>key_name</replaceable>; </optional>
<optional> session-keyalg <replaceable>algorithm_id</replaceable>; </optional>
<optional> memstatistics <replaceable>yes_or_no</replaceable>; </optional>
<optional> memstatistics-file <replaceable>path_name</replaceable>; </optional>
<optional> pid-file <replaceable>path_name</replaceable>; </optional>
<optional> recursing-file <replaceable>path_name</replaceable>; </optional>
<optional> statistics-file <replaceable>path_name</replaceable>; </optional>
<optional> zone-statistics <replaceable>yes_or_no</replaceable>; </optional>
<optional> auth-nxdomain <replaceable>yes_or_no</replaceable>; </optional>
<optional> deallocate-on-exit <replaceable>yes_or_no</replaceable>; </optional>
<optional> dialup <replaceable>dialup_option</replaceable>; </optional>
<optional> fake-iquery <replaceable>yes_or_no</replaceable>; </optional>
<optional> fetch-glue <replaceable>yes_or_no</replaceable>; </optional>
<optional> flush-zones-on-shutdown <replaceable>yes_or_no</replaceable>; </optional>
<optional> has-old-clients <replaceable>yes_or_no</replaceable>; </optional>
<optional> host-statistics <replaceable>yes_or_no</replaceable>; </optional>
<optional> host-statistics-max <replaceable>number</replaceable>; </optional>
<optional> minimal-responses <replaceable>yes_or_no</replaceable>; </optional>
<optional> multiple-cnames <replaceable>yes_or_no</replaceable>; </optional>
<optional> notify <replaceable>yes_or_no</replaceable> | <replaceable>explicit</replaceable> | <replaceable>master-only</replaceable>; </optional>
<optional> recursion <replaceable>yes_or_no</replaceable>; </optional>
<optional> rfc2308-type1 <replaceable>yes_or_no</replaceable>; </optional>
<optional> use-id-pool <replaceable>yes_or_no</replaceable>; </optional>
<optional> maintain-ixfr-base <replaceable>yes_or_no</replaceable>; </optional>
<optional> ixfr-from-differences (<replaceable>yes_or_no</replaceable> | <constant>master</constant> | <constant>slave</constant>); </optional>
<optional> dnssec-enable <replaceable>yes_or_no</replaceable>; </optional>
<optional> dnssec-validation (<replaceable>yes_or_no</replaceable> | <constant>auto</constant>); </optional>
<optional> dnssec-lookaside ( <replaceable>auto</replaceable> |
<replaceable>no</replaceable> |
<replaceable>domain</replaceable> trust-anchor <replaceable>domain</replaceable> ); </optional>
<optional> dnssec-must-be-secure <replaceable>domain yes_or_no</replaceable>; </optional>
<optional> dnssec-accept-expired <replaceable>yes_or_no</replaceable>; </optional>
<optional> forward ( <replaceable>only</replaceable> | <replaceable>first</replaceable> ); </optional>
<optional> forwarders { <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> dual-stack-servers <optional>port <replaceable>ip_port</replaceable></optional> {
( <replaceable>domain_name</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> |
<replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ) ;
... }; </optional>
<optional> check-names ( <replaceable>master</replaceable> | <replaceable>slave</replaceable> | <replaceable>response</replaceable> )
( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
<optional> check-dup-records ( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
<optional> check-mx ( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
<optional> check-wildcard <replaceable>yes_or_no</replaceable>; </optional>
<optional> check-integrity <replaceable>yes_or_no</replaceable>; </optional>
<optional> check-mx-cname ( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
<optional> check-srv-cname ( <replaceable>warn</replaceable> | <replaceable>fail</replaceable> | <replaceable>ignore</replaceable> ); </optional>
<optional> check-sibling <replaceable>yes_or_no</replaceable>; </optional>
<optional> allow-new-zones { <replaceable>yes_or_no</replaceable> }; </optional>
<optional> allow-notify { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query-on { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query-cache { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query-cache-on { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-transfer { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-recursion { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-recursion-on { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-update { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-update-forwarding { <replaceable>address_match_list</replaceable> }; </optional>
<optional> update-check-ksk <replaceable>yes_or_no</replaceable>; </optional>
<optional> dnssec-dnskey-kskonly <replaceable>yes_or_no</replaceable>; </optional>
<optional> dnssec-secure-to-insecure <replaceable>yes_or_no</replaceable> ;</optional>
<optional> try-tcp-refresh <replaceable>yes_or_no</replaceable>; </optional>
<optional> allow-v6-synthesis { <replaceable>address_match_list</replaceable> }; </optional>
<optional> blackhole { <replaceable>address_match_list</replaceable> }; </optional>
<optional> use-v4-udp-ports { <replaceable>port_list</replaceable> }; </optional>
<optional> avoid-v4-udp-ports { <replaceable>port_list</replaceable> }; </optional>
<optional> use-v6-udp-ports { <replaceable>port_list</replaceable> }; </optional>
<optional> avoid-v6-udp-ports { <replaceable>port_list</replaceable> }; </optional>
<optional> listen-on <optional> port <replaceable>ip_port</replaceable> </optional> { <replaceable>address_match_list</replaceable> }; </optional>
<optional> listen-on-v6 <optional> port <replaceable>ip_port</replaceable> </optional> { <replaceable>address_match_list</replaceable> }; </optional>
<optional> query-source ( ( <replaceable>ip4_addr</replaceable> | <replaceable>*</replaceable> )
<optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional> |
<optional> address ( <replaceable>ip4_addr</replaceable> | <replaceable>*</replaceable> ) </optional>
<optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional> ) ; </optional>
<optional> query-source-v6 ( ( <replaceable>ip6_addr</replaceable> | <replaceable>*</replaceable> )
<optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional> |
<optional> address ( <replaceable>ip6_addr</replaceable> | <replaceable>*</replaceable> ) </optional>
<optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional> ) ; </optional>
<optional> use-queryport-pool <replaceable>yes_or_no</replaceable>; </optional>
<optional> queryport-pool-ports <replaceable>number</replaceable>; </optional>
<optional> queryport-pool-updateinterval <replaceable>number</replaceable>; </optional>
<optional> max-transfer-time-in <replaceable>number</replaceable>; </optional>
<optional> max-transfer-time-out <replaceable>number</replaceable>; </optional>
<optional> max-transfer-idle-in <replaceable>number</replaceable>; </optional>
<optional> max-transfer-idle-out <replaceable>number</replaceable>; </optional>
<optional> tcp-clients <replaceable>number</replaceable>; </optional>
<optional> reserved-sockets <replaceable>number</replaceable>; </optional>
<optional> recursive-clients <replaceable>number</replaceable>; </optional>
<optional> serial-query-rate <replaceable>number</replaceable>; </optional>
<optional> serial-queries <replaceable>number</replaceable>; </optional>
<optional> tcp-listen-queue <replaceable>number</replaceable>; </optional>
<optional> transfer-format <replaceable>( one-answer | many-answers )</replaceable>; </optional>
<optional> transfers-in <replaceable>number</replaceable>; </optional>
<optional> transfers-out <replaceable>number</replaceable>; </optional>
<optional> transfers-per-ns <replaceable>number</replaceable>; </optional>
<optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> alt-transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> alt-transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>)
<optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> use-alt-transfer-source <replaceable>yes_or_no</replaceable>; </optional>
<optional> notify-delay <replaceable>seconds</replaceable> ; </optional>
<optional> notify-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> notify-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> notify-to-soa <replaceable>yes_or_no</replaceable> ; </optional>
<optional> also-notify { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ;
<optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> max-ixfr-log-size <replaceable>number</replaceable>; </optional>
<optional> max-journal-size <replaceable>size_spec</replaceable>; </optional>
<optional> coresize <replaceable>size_spec</replaceable> ; </optional>
<optional> datasize <replaceable>size_spec</replaceable> ; </optional>
<optional> files <replaceable>size_spec</replaceable> ; </optional>
<optional> stacksize <replaceable>size_spec</replaceable> ; </optional>
<optional> cleaning-interval <replaceable>number</replaceable>; </optional>
<optional> heartbeat-interval <replaceable>number</replaceable>; </optional>
<optional> interface-interval <replaceable>number</replaceable>; </optional>
<optional> statistics-interval <replaceable>number</replaceable>; </optional>
<optional> topology { <replaceable>address_match_list</replaceable> }</optional>;
<optional> sortlist { <replaceable>address_match_list</replaceable> }</optional>;
<optional> rrset-order { <replaceable>order_spec</replaceable> ; <optional> <replaceable>order_spec</replaceable> ; ... </optional> </optional> };
<optional> lame-ttl <replaceable>number</replaceable>; </optional>
<optional> max-ncache-ttl <replaceable>number</replaceable>; </optional>
<optional> max-cache-ttl <replaceable>number</replaceable>; </optional>
<optional> sig-validity-interval <replaceable>number</replaceable> <optional><replaceable>number</replaceable></optional> ; </optional>
<optional> sig-signing-nodes <replaceable>number</replaceable> ; </optional>
<optional> sig-signing-signatures <replaceable>number</replaceable> ; </optional>
<optional> sig-signing-type <replaceable>number</replaceable> ; </optional>
<optional> min-roots <replaceable>number</replaceable>; </optional>
<optional> use-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
<optional> provide-ixfr <replaceable>yes_or_no</replaceable>; </optional>
<optional> request-ixfr <replaceable>yes_or_no</replaceable>; </optional>
<optional> treat-cr-as-space <replaceable>yes_or_no</replaceable> ; </optional>
<optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> min-retry-time <replaceable>number</replaceable> ; </optional>
<optional> max-retry-time <replaceable>number</replaceable> ; </optional>
<optional> port <replaceable>ip_port</replaceable>; </optional>
<optional> additional-from-auth <replaceable>yes_or_no</replaceable> ; </optional>
<optional> additional-from-cache <replaceable>yes_or_no</replaceable> ; </optional>
<optional> random-device <replaceable>path_name</replaceable> ; </optional>
<optional> max-cache-size <replaceable>size_spec</replaceable> ; </optional>
<optional> match-mapped-addresses <replaceable>yes_or_no</replaceable>; </optional>
<optional> filter-aaaa-on-v4 ( <replaceable>yes_or_no</replaceable> | <replaceable>break-dnssec</replaceable> ); </optional>
<optional> filter-aaaa { <replaceable>address_match_list</replaceable> }; </optional>
<optional> dns64 <replaceable>IPv6-prefix</replaceable> {
<optional> clients { <replaceable>address_match_list</replaceable> }; </optional>
<optional> mapped { <replaceable>address_match_list</replaceable> }; </optional>
<optional> exclude { <replaceable>address_match_list</replaceable> }; </optional>
<optional> suffix IPv6-address; </optional>
<optional> recursive-only <replaceable>yes_or_no</replaceable>; </optional>
<optional> break-dnssec <replaceable>yes_or_no</replaceable>; </optional>
}; </optional>;
<optional> dns64-server <replaceable>name</replaceable> </optional>
<optional> dns64-contact <replaceable>name</replaceable> </optional>
<optional> preferred-glue ( <replaceable>A</replaceable> | <replaceable>AAAA</replaceable> | <replaceable>NONE</replaceable> ); </optional>
<optional> edns-udp-size <replaceable>number</replaceable>; </optional>
<optional> max-udp-size <replaceable>number</replaceable>; </optional>
<optional> root-delegation-only <optional> exclude { <replaceable>namelist</replaceable> } </optional> ; </optional>
<optional> querylog <replaceable>yes_or_no</replaceable> ; </optional>
<optional> disable-algorithms <replaceable>domain</replaceable> { <replaceable>algorithm</replaceable>;
<optional> <replaceable>algorithm</replaceable>; </optional> }; </optional>
<optional> acache-enable <replaceable>yes_or_no</replaceable> ; </optional>
<optional> acache-cleaning-interval <replaceable>number</replaceable>; </optional>
<optional> max-acache-size <replaceable>size_spec</replaceable> ; </optional>
<optional> clients-per-query <replaceable>number</replaceable> ; </optional>
<optional> max-clients-per-query <replaceable>number</replaceable> ; </optional>
<optional> max-recursion-depth <replaceable>number</replaceable> ; </optional>
<optional> max-recursion-queries <replaceable>number</replaceable> ; </optional>
<optional> masterfile-format (<constant>text</constant>|<constant>raw</constant>) ; </optional>
<optional> empty-server <replaceable>name</replaceable> ; </optional>
<optional> empty-contact <replaceable>name</replaceable> ; </optional>
<optional> empty-zones-enable <replaceable>yes_or_no</replaceable> ; </optional>
<optional> disable-empty-zone <replaceable>zone_name</replaceable> ; </optional>
<optional> zero-no-soa-ttl <replaceable>yes_or_no</replaceable> ; </optional>
<optional> zero-no-soa-ttl-cache <replaceable>yes_or_no</replaceable> ; </optional>
<optional> resolver-query-timeout <replaceable>number</replaceable> ; </optional>
<optional> deny-answer-addresses { <replaceable>address_match_list</replaceable> } <optional> except-from { <replaceable>namelist</replaceable> } </optional>;</optional>
<optional> deny-answer-aliases { <replaceable>namelist</replaceable> } <optional> except-from { <replaceable>namelist</replaceable> } </optional>;</optional>
<optional> rate-limit {
<optional> responses-per-second <replaceable>number</replaceable> ; </optional>
<optional> referrals-per-second <replaceable>number</replaceable> ; </optional>
<optional> nodata-per-second <replaceable>number</replaceable> ; </optional>
<optional> errors-per-second <replaceable>number</replaceable> ; </optional>
<optional> nxdomains-per-second <replaceable>number</replaceable> ; </optional>
<optional> all-per-second <replaceable>number</replaceable> ; </optional>
<optional> window <replaceable>number</replaceable> ; </optional>
<optional> log-only <replaceable>yes_or_no</replaceable> ; </optional>
<optional> qps-scale <replaceable>number</replaceable> ; </optional>
<optional> IPv4-prefix-length <replaceable>number</replaceable> ; </optional>
<optional> IPv6-prefix-length <replaceable>number</replaceable> ; </optional>
<optional> slip <replaceable>number</replaceable> ; </optional>
<optional> exempt-clients { <replaceable>address_match_list</replaceable> } ; </optional>
<optional> max-table-size <replaceable>number</replaceable> ; </optional>
<optional> min-table-size <replaceable>number</replaceable> ; </optional>
} ; </optional>
<optional> response-policy { <replaceable>zone_name</replaceable> <optional> policy given | disabled | passthru | nxdomain | nodata | cname <replaceable>domain</replaceable> </optional> ; } ; </optional>
};
</programlisting>
</sect2>
<sect2 id="options">
<title><command>options</command> Statement Definition and
Usage</title>
<para>
The <command>options</command> statement sets up global
options
to be used by <acronym>BIND</acronym>. This statement
may appear only
once in a configuration file. If there is no <command>options</command>
statement, an options block with each option set to its default will
be used.
</para>
<variablelist>
<varlistentry>
<term><command>attach-cache</command></term>
<listitem>
<para>
Allows multiple views to share a single cache
database.
Each view has its own cache database by default, but
if multiple views have the same operational policy
for name resolution and caching, those views can
share a single cache to save memory and possibly
improve resolution efficiency by using this option.
</para>
<para>
The <command>attach-cache</command> option
may also be specified in <command>view</command>
statements, in which case it overrides the
global <command>attach-cache</command> option.
</para>
<para>
The <replaceable>cache_name</replaceable> specifies
the cache to be shared.
When the <command>named</command> server configures
views which are supposed to share a cache, it
creates a cache with the specified name for the
first view of these sharing views.
The rest of the views will simply refer to the
already created cache.
</para>
<para>
One common configuration to share a cache would be to
allow all views to share a single cache.
This can be done by specifying
the <command>attach-cache</command> as a global
option with an arbitrary name.
</para>
<para>
Another possible operation is to allow a subset of
all views to share a cache while the others to
retain their own caches.
For example, if there are three views A, B, and C,
and only A and B should share a cache, specify the
<command>attach-cache</command> option as a view A (or
B)'s option, referring to the other view name:
</para>
<programlisting>
view "A" {
// this view has its own cache
...
};
view "B" {
// this view refers to A's cache
attach-cache "A";
};
view "C" {
// this view has its own cache
...
};
</programlisting>
<para>
Views that share a cache must have the same policy
on configurable parameters that may affect caching.
The current implementation requires the following
configurable options be consistent among these
views:
<command>check-names</command>,
<command>cleaning-interval</command>,
<command>dnssec-accept-expired</command>,
<command>dnssec-validation</command>,
<command>max-cache-ttl</command>,
<command>max-ncache-ttl</command>,
<command>max-cache-size</command>, and
<command>zero-no-soa-ttl</command>.
</para>
<para>
Note that there may be other parameters that may
cause confusion if they are inconsistent for
different views that share a single cache.
For example, if these views define different sets of
forwarders that can return different answers for the
same question, sharing the answer does not make
sense or could even be harmful.
It is administrator's responsibility to ensure
configuration differences in different views do
not cause disruption with a shared cache.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>directory</command></term>
<listitem>
<para>
The working directory of the server.
Any non-absolute pathnames in the configuration file will be
taken
as relative to this directory. The default location for most
server
output files (e.g. <filename>named.run</filename>)
is this directory.
If a directory is not specified, the working directory
defaults to `<filename>.</filename>', the directory from
which the server
was started. The directory specified should be an absolute
path.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>key-directory</command></term>
<listitem>
<para>
When performing dynamic update of secure zones, the
directory where the public and private DNSSEC key files
should be found, if different than the current working
directory. (Note that this option has no effect on the
paths for files containing non-DNSSEC keys such as
<filename>bind.keys</filename>,
<filename>rndc.key</filename> or
<filename>session.key</filename>.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>managed-keys-directory</command></term>
<listitem>
<para>
The directory used to hold the files used to track managed keys.
By default it is the working directory. It there are no
views then the file <filename>managed-keys.bind</filename>
otherwise a SHA256 hash of the view name is used with
<filename>.mkeys</filename> extension added.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>named-xfer</command></term>
<listitem>
<para>
<emphasis>This option is obsolete.</emphasis> It
was used in <acronym>BIND</acronym> 8 to specify
the pathname to the <command>named-xfer</command>
program. In <acronym>BIND</acronym> 9, no separate
<command>named-xfer</command> program is needed;
its functionality is built into the name server.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tkey-gssapi-keytab</command></term>
<listitem>
<para>
The KRB5 keytab file to use for GSS-TSIG updates. If
this option is set and tkey-gssapi-credential is not
set, then updates will be allowed with any key
matching a principal in the specified keytab.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tkey-gssapi-credential</command></term>
<listitem>
<para>
The security credential with which the server should
authenticate keys requested by the GSS-TSIG protocol.
Currently only Kerberos 5 authentication is available
and the credential is a Kerberos principal which the
server can acquire through the default system key
file, normally <filename>/etc/krb5.keytab</filename>.
The location keytab file can be overridden using the
tkey-gssapi-keytab option. Normally this principal is
of the form "<userinput>DNS/</userinput><varname>server.domain</varname>".
To use GSS-TSIG, <command>tkey-domain</command> must
also be set if a specific keytab is not set with
tkey-gssapi-keytab.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tkey-domain</command></term>
<listitem>
<para>
The domain appended to the names of all shared keys
generated with <command>TKEY</command>. When a
client requests a <command>TKEY</command> exchange,
it may or may not specify the desired name for the
key. If present, the name of the shared key will
be <varname>client specified part</varname> +
<varname>tkey-domain</varname>. Otherwise, the
name of the shared key will be <varname>random hex
digits</varname> + <varname>tkey-domain</varname>.
In most cases, the <command>domainname</command>
should be the server's domain name, or an otherwise
non-existent subdomain like
"_tkey.<varname>domainname</varname>". If you are
using GSS-TSIG, this variable must be defined, unless
you specify a specific keytab using tkey-gssapi-keytab.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tkey-dhkey</command></term>
<listitem>
<para>
The Diffie-Hellman key used by the server
to generate shared keys with clients using the Diffie-Hellman
mode
of <command>TKEY</command>. The server must be
able to load the
public and private keys from files in the working directory.
In
most cases, the keyname should be the server's host name.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>cache-file</command></term>
<listitem>
<para>
This is for testing only. Do not use.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dump-file</command></term>
<listitem>
<para>
The pathname of the file the server dumps
the database to when instructed to do so with
<command>rndc dumpdb</command>.
If not specified, the default is <filename>named_dump.db</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>memstatistics-file</command></term>
<listitem>
<para>
The pathname of the file the server writes memory
usage statistics to on exit. If not specified,
the default is <filename>named.memstats</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>pid-file</command></term>
<listitem>
<para>
The pathname of the file the server writes its process ID
in. If not specified, the default is
<filename>/var/run/named/named.pid</filename>.
The PID file is used by programs that want to send signals to
the running
name server. Specifying <command>pid-file none</command> disables the
use of a PID file — no file will be written and any
existing one will be removed. Note that <command>none</command>
is a keyword, not a filename, and therefore is not enclosed
in
double quotes.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>recursing-file</command></term>
<listitem>
<para>
The pathname of the file the server dumps
the queries that are currently recursing when instructed
to do so with <command>rndc recursing</command>.
If not specified, the default is <filename>named.recursing</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>statistics-file</command></term>
<listitem>
<para>
The pathname of the file the server appends statistics
to when instructed to do so using <command>rndc stats</command>.
If not specified, the default is <filename>named.stats</filename> in the
server's current directory. The format of the file is
described
in <xref linkend="statsfile"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>bindkeys-file</command></term>
<listitem>
<para>
The pathname of a file to override the built-in trusted
keys provided by <command>named</command>.
See the discussion of <command>dnssec-lookaside</command>
and <command>dnssec-validation</command> for details.
If not specified, the default is
<filename>/etc/bind.keys</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>secroots-file</command></term>
<listitem>
<para>
The pathname of the file the server dumps
security roots to when instructed to do so with
<command>rndc secroots</command>.
If not specified, the default is
<filename>named.secroots</filename>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>session-keyfile</command></term>
<listitem>
<para>
The pathname of the file into which to write a TSIG
session key generated by <command>named</command> for use by
<command>nsupdate -l</command>. If not specified, the
default is <filename>/var/run/named/session.key</filename>.
(See <xref linkend="dynamic_update_policies"/>, and in
particular the discussion of the
<command>update-policy</command> statement's
<userinput>local</userinput> option for more
information about this feature.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>session-keyname</command></term>
<listitem>
<para>
The key name to use for the TSIG session key.
If not specified, the default is "local-ddns".
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>session-keyalg</command></term>
<listitem>
<para>
The algorithm to use for the TSIG session key.
Valid values are hmac-sha1, hmac-sha224, hmac-sha256,
hmac-sha384, hmac-sha512 and hmac-md5. If not
specified, the default is hmac-sha256.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>port</command></term>
<listitem>
<para>
The UDP/TCP port number the server uses for
receiving and sending DNS protocol traffic.
The default is 53. This option is mainly intended for server
testing;
a server using a port other than 53 will not be able to
communicate with
the global DNS.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>random-device</command></term>
<listitem>
<para>
The source of entropy to be used by the server. Entropy is
primarily needed
for DNSSEC operations, such as TKEY transactions and dynamic
update of signed
zones. This options specifies the device (or file) from which
to read
entropy. If this is a file, operations requiring entropy will
fail when the
file has been exhausted. If not specified, the default value
is
<filename>/dev/random</filename>
(or equivalent) when present, and none otherwise. The
<command>random-device</command> option takes
effect during
the initial configuration load at server startup time and
is ignored on subsequent reloads.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>preferred-glue</command></term>
<listitem>
<para>
If specified, the listed type (A or AAAA) will be emitted
before other glue
in the additional section of a query response.
The default is not to prefer any type (NONE).
</para>
</listitem>
</varlistentry>
<varlistentry id="root_delegation_only">
<term><command>root-delegation-only</command></term>
<listitem>
<para>
Turn on enforcement of delegation-only in TLDs
(top level domains) and root zones with an optional
exclude list.
</para>
<para>
DS queries are expected to be made to and be answered by
delegation only zones. Such queries and responses are
treated as an exception to delegation-only processing
and are not converted to NXDOMAIN responses provided
a CNAME is not discovered at the query name.
</para>
<para>
If a delegation only zone server also serves a child
zone it is not always possible to determine whether
an answer comes from the delegation only zone or the
child zone. SOA NS and DNSKEY records are apex
only records and a matching response that contains
these records or DS is treated as coming from a
child zone. RRSIG records are also examined to see
if they are signed by a child zone or not. The
authority section is also examined to see if there
is evidence that the answer is from the child zone.
Answers that are determined to be from a child zone
are not converted to NXDOMAIN responses. Despite
all these checks there is still a possibility of
false negatives when a child zone is being served.
</para>
<para>
Similarly false positives can arise from empty nodes
(no records at the name) in the delegation only zone
when the query type is not ANY.
</para>
<para>
Note some TLDs are not delegation only (e.g. "DE", "LV",
"US" and "MUSEUM"). This list is not exhaustive.
</para>
<programlisting>
options {
root-delegation-only exclude { "de"; "lv"; "us"; "museum"; };
};
</programlisting>
</listitem>
</varlistentry>
<varlistentry>
<term><command>disable-algorithms</command></term>
<listitem>
<para>
Disable the specified DNSSEC algorithms at and below the
specified name.
Multiple <command>disable-algorithms</command>
statements are allowed.
Only the most specific will be applied.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-lookaside</command></term>
<listitem>
<para>
When set, <command>dnssec-lookaside</command> provides the
validator with an alternate method to validate DNSKEY
records at the top of a zone. When a DNSKEY is at or
below a domain specified by the deepest
<command>dnssec-lookaside</command>, and the normal DNSSEC
validation has left the key untrusted, the trust-anchor
will be appended to the key name and a DLV record will be
looked up to see if it can validate the key. If the DLV
record validates a DNSKEY (similarly to the way a DS
record does) the DNSKEY RRset is deemed to be trusted.
</para>
<para>
If <command>dnssec-lookaside</command> is set to
<userinput>auto</userinput>, then built-in default
values for the DLV domain and trust anchor will be
used, along with a built-in key for validation.
</para>
<para>
If <command>dnssec-lookaside</command> is set to
<userinput>no</userinput>, then dnssec-lookaside
is not used.
</para>
<para>
The default DLV key is stored in the file
<filename>bind.keys</filename>;
<command>named</command> will load that key at
startup if <command>dnssec-lookaside</command> is set to
<constant>auto</constant>. A copy of the file is
installed along with <acronym>BIND</acronym> 9, and is
current as of the release date. If the DLV key expires, a
new copy of <filename>bind.keys</filename> can be downloaded
from <ulink>https://www.isc.org/solutions/dlv</ulink>.
</para>
<para>
(To prevent problems if <filename>bind.keys</filename> is
not found, the current key is also compiled in to
<command>named</command>. Relying on this is not
recommended, however, as it requires <command>named</command>
to be recompiled with a new key when the DLV key expires.)
</para>
<para>
NOTE: <command>named</command> only loads certain specific
keys from <filename>bind.keys</filename>: those for the
DLV zone and for the DNS root zone. The file cannot be
used to store keys for other zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-must-be-secure</command></term>
<listitem>
<para>
Specify hierarchies which must be or may not be secure
(signed and validated). If <userinput>yes</userinput>,
then <command>named</command> will only accept answers if
they are secure. If <userinput>no</userinput>, then normal
DNSSEC validation applies allowing for insecure answers to
be accepted. The specified domain must be under a
<command>trusted-keys</command> or
<command>managed-keys</command> statement, or
<command>dnssec-lookaside</command> must be active.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dns64</command></term>
<listitem>
<para>
This directive instructs <command>named</command> to
return mapped IPv4 addresses to AAAA queries when
there are no AAAA records. It is intended to be
used in conjunction with a NAT64. Each
<command>dns64</command> defines one DNS64 prefix.
Multiple DNS64 prefixes can be defined.
</para>
<para>
Compatible IPv6 prefixes have lengths of 32, 40, 48, 56,
64 and 96 as per RFC 6052.
</para>
<para>
Additionally a reverse IP6.ARPA zone will be created for
the prefix to provide a mapping from the IP6.ARPA names
to the corresponding IN-ADDR.ARPA names using synthesized
CNAMEs. <command>dns64-server</command> and
<command>dns64-contact</command> can be used to specify
the name of the server and contact for the zones. These
are settable at the view / options level. These are
not settable on a per-prefix basis.
</para>
<para>
Each <command>dns64</command> supports an optional
<command>clients</command> ACL that determines which
clients are affected by this directive. If not defined,
it defaults to <userinput>any;</userinput>.
</para>
<para>
Each <command>dns64</command> supports an optional
<command>mapped</command> ACL that selects which
IPv4 addresses are to be mapped in the corresponding
A RRset. If not defined it defaults to
<userinput>any;</userinput>.
</para>
<para>
Normally, DNS64 won't apply to a domain name that
owns one or more AAAA records; these records will
simply be returned. The optional
<command>exclude</command> ACL allows specification
of a list of IPv6 addresses that will be ignored
if they appear in a domain name's AAAA records, and
DNS64 will be applied to any A records the domain
name owns. If not defined, <command>exclude</command>
defaults to none.
</para>
<para>
A optional <command>suffix</command> can also
be defined to set the bits trailing the mapped
IPv4 address bits. By default these bits are
set to <userinput>::</userinput>. The bits
matching the prefix and mapped IPv4 address
must be zero.
</para>
<para>
If <command>recursive-only</command> is set to
<command>yes</command> the DNS64 synthesis will
only happen for recursive queries. The default
is <command>no</command>.
</para>
<para>
If <command>break-dnssec</command> is set to
<command>yes</command> the DNS64 synthesis will
happen even if the result, if validated, would
cause a DNSSEC validation failure. If this option
is set to <command>no</command> (the default), the DO
is set on the incoming query, and there are RRSIGs on
the applicable records, then synthesis will not happen.
</para>
<programlisting>
acl rfc1918 { 10/8; 192.168/16; 172.16/12; };
dns64 64:FF9B::/96 {
clients { any; };
mapped { !rfc1918; any; };
exclude { 64:FF9B::/96; ::ffff:0000:0000/96; };
suffix ::;
};
</programlisting>
</listitem>
</varlistentry>
</variablelist>
<sect3 id="boolean_options">
<title>Boolean Options</title>
<variablelist>
<varlistentry>
<term><command>allow-new-zones</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then zones can be
added at runtime via <command>rndc addzone</command>
or deleted via <command>rndc delzone</command>.
The default is <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>auth-nxdomain</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then the <command>AA</command> bit
is always set on NXDOMAIN responses, even if the server is
not actually
authoritative. The default is <userinput>no</userinput>;
this is
a change from <acronym>BIND</acronym> 8. If you
are using very old DNS software, you
may need to set it to <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>deallocate-on-exit</command></term>
<listitem>
<para>
This option was used in <acronym>BIND</acronym>
8 to enable checking
for memory leaks on exit. <acronym>BIND</acronym> 9 ignores the option and always performs
the checks.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>memstatistics</command></term>
<listitem>
<para>
Write memory statistics to the file specified by
<command>memstatistics-file</command> at exit.
The default is <userinput>no</userinput> unless
'-m record' is specified on the command line in
which case it is <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dialup</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then the
server treats all zones as if they are doing zone transfers
across
a dial-on-demand dialup link, which can be brought up by
traffic
originating from this server. This has different effects
according
to zone type and concentrates the zone maintenance so that
it all
happens in a short interval, once every <command>heartbeat-interval</command> and
hopefully during the one call. It also suppresses some of
the normal
zone maintenance traffic. The default is <userinput>no</userinput>.
</para>
<para>
The <command>dialup</command> option
may also be specified in the <command>view</command> and
<command>zone</command> statements,
in which case it overrides the global <command>dialup</command>
option.
</para>
<para>
If the zone is a master zone, then the server will send out a
NOTIFY
request to all the slaves (default). This should trigger the
zone serial
number check in the slave (providing it supports NOTIFY)
allowing the slave
to verify the zone while the connection is active.
The set of servers to which NOTIFY is sent can be controlled
by
<command>notify</command> and <command>also-notify</command>.
</para>
<para>
If the
zone is a slave or stub zone, then the server will suppress
the regular
"zone up to date" (refresh) queries and only perform them
when the
<command>heartbeat-interval</command> expires in
addition to sending
NOTIFY requests.
</para>
<para>
Finer control can be achieved by using
<userinput>notify</userinput> which only sends NOTIFY
messages,
<userinput>notify-passive</userinput> which sends NOTIFY
messages and
suppresses the normal refresh queries, <userinput>refresh</userinput>
which suppresses normal refresh processing and sends refresh
queries
when the <command>heartbeat-interval</command>
expires, and
<userinput>passive</userinput> which just disables normal
refresh
processing.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="4" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="1.150in"/>
<colspec colname="4" colnum="4" colsep="0" colwidth="1.150in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
dialup mode
</para>
</entry>
<entry colname="2">
<para>
normal refresh
</para>
</entry>
<entry colname="3">
<para>
heart-beat refresh
</para>
</entry>
<entry colname="4">
<para>
heart-beat notify
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>no</command> (default)</para>
</entry>
<entry colname="2">
<para>
yes
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
no
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>yes</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
yes
</para>
</entry>
<entry colname="4">
<para>
yes
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>notify</command></para>
</entry>
<entry colname="2">
<para>
yes
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
yes
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>refresh</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
yes
</para>
</entry>
<entry colname="4">
<para>
no
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>passive</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
no
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>notify-passive</command></para>
</entry>
<entry colname="2">
<para>
no
</para>
</entry>
<entry colname="3">
<para>
no
</para>
</entry>
<entry colname="4">
<para>
yes
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
Note that normal NOTIFY processing is not affected by
<command>dialup</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>fake-iquery</command></term>
<listitem>
<para>
In <acronym>BIND</acronym> 8, this option
enabled simulating the obsolete DNS query type
IQUERY. <acronym>BIND</acronym> 9 never does
IQUERY simulation.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>fetch-glue</command></term>
<listitem>
<para>
This option is obsolete.
In BIND 8, <userinput>fetch-glue yes</userinput>
caused the server to attempt to fetch glue resource records
it
didn't have when constructing the additional
data section of a response. This is now considered a bad
idea
and BIND 9 never does it.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>flush-zones-on-shutdown</command></term>
<listitem>
<para>
When the nameserver exits due receiving SIGTERM,
flush or do not flush any pending zone writes. The default
is
<command>flush-zones-on-shutdown</command> <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>has-old-clients</command></term>
<listitem>
<para>
This option was incorrectly implemented
in <acronym>BIND</acronym> 8, and is ignored by <acronym>BIND</acronym> 9.
To achieve the intended effect
of
<command>has-old-clients</command> <userinput>yes</userinput>, specify
the two separate options <command>auth-nxdomain</command> <userinput>yes</userinput>
and <command>rfc2308-type1</command> <userinput>no</userinput> instead.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>host-statistics</command></term>
<listitem>
<para>
In BIND 8, this enables keeping of
statistics for every host that the name server interacts
with.
Not implemented in BIND 9.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>maintain-ixfr-base</command></term>
<listitem>
<para>
<emphasis>This option is obsolete</emphasis>.
It was used in <acronym>BIND</acronym> 8 to
determine whether a transaction log was
kept for Incremental Zone Transfer. <acronym>BIND</acronym> 9 maintains a transaction
log whenever possible. If you need to disable outgoing
incremental zone
transfers, use <command>provide-ixfr</command> <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>minimal-responses</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then when generating
responses the server will only add records to the authority
and additional data sections when they are required (e.g.
delegations, negative responses). This may improve the
performance of the server.
The default is <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>multiple-cnames</command></term>
<listitem>
<para>
This option was used in <acronym>BIND</acronym> 8 to allow
a domain name to have multiple CNAME records in violation of
the DNS standards. <acronym>BIND</acronym> 9.2 onwards
always strictly enforces the CNAME rules both in master
files and dynamic updates.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify</command></term>
<listitem>
<para>
If <userinput>yes</userinput> (the default),
DNS NOTIFY messages are sent when a zone the server is
authoritative for
changes, see <xref linkend="notify"/>. The messages are
sent to the
servers listed in the zone's NS records (except the master
server identified
in the SOA MNAME field), and to any servers listed in the
<command>also-notify</command> option.
</para>
<para>
If <userinput>master-only</userinput>, notifies are only
sent
for master zones.
If <userinput>explicit</userinput>, notifies are sent only
to
servers explicitly listed using <command>also-notify</command>.
If <userinput>no</userinput>, no notifies are sent.
</para>
<para>
The <command>notify</command> option may also be
specified in the <command>zone</command>
statement,
in which case it overrides the <command>options notify</command> statement.
It would only be necessary to turn off this option if it
caused slaves
to crash.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-to-soa</command></term>
<listitem>
<para>
If <userinput>yes</userinput> do not check the nameservers
in the NS RRset against the SOA MNAME. Normally a NOTIFY
message is not sent to the SOA MNAME (SOA ORIGIN) as it is
supposed to contain the name of the ultimate master.
Sometimes, however, a slave is listed as the SOA MNAME in
hidden master configurations and in that case you would
want the ultimate master to still send NOTIFY messages to
all the nameservers listed in the NS RRset.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>recursion</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, and a
DNS query requests recursion, then the server will attempt
to do
all the work required to answer the query. If recursion is
off
and the server does not already know the answer, it will
return a
referral response. The default is
<userinput>yes</userinput>.
Note that setting <command>recursion no</command> does not prevent
clients from getting data from the server's cache; it only
prevents new data from being cached as an effect of client
queries.
Caching may still occur as an effect the server's internal
operation, such as NOTIFY address lookups.
See also <command>fetch-glue</command> above.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>rfc2308-type1</command></term>
<listitem>
<para>
Setting this to <userinput>yes</userinput> will
cause the server to send NS records along with the SOA
record for negative
answers. The default is <userinput>no</userinput>.
</para>
<note>
<simpara>
Not yet implemented in <acronym>BIND</acronym>
9.
</simpara>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-id-pool</command></term>
<listitem>
<para>
<emphasis>This option is obsolete</emphasis>.
<acronym>BIND</acronym> 9 always allocates query
IDs from a pool.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zone-statistics</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, the server will collect
statistical data on all zones (unless specifically turned
off
on a per-zone basis by specifying <command>zone-statistics no</command>
in the <command>zone</command> statement).
The default is <userinput>no</userinput>.
These statistics may be accessed
using <command>rndc stats</command>, which will
dump them to the file listed
in the <command>statistics-file</command>. See
also <xref linkend="statsfile"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-ixfr</command></term>
<listitem>
<para>
<emphasis>This option is obsolete</emphasis>.
If you need to disable IXFR to a particular server or
servers, see
the information on the <command>provide-ixfr</command> option
in <xref linkend="server_statement_definition_and_usage"/>.
See also
<xref linkend="incremental_zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>provide-ixfr</command></term>
<listitem>
<para>
See the description of
<command>provide-ixfr</command> in
<xref linkend="server_statement_definition_and_usage"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>request-ixfr</command></term>
<listitem>
<para>
See the description of
<command>request-ixfr</command> in
<xref linkend="server_statement_definition_and_usage"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>treat-cr-as-space</command></term>
<listitem>
<para>
This option was used in <acronym>BIND</acronym>
8 to make
the server treat carriage return ("<command>\r</command>") characters the same way
as a space or tab character,
to facilitate loading of zone files on a UNIX system that
were generated
on an NT or DOS machine. In <acronym>BIND</acronym> 9, both UNIX "<command>\n</command>"
and NT/DOS "<command>\r\n</command>" newlines
are always accepted,
and the option is ignored.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>additional-from-auth</command></term>
<term><command>additional-from-cache</command></term>
<listitem>
<para>
These options control the behavior of an authoritative
server when
answering queries which have additional data, or when
following CNAME
and DNAME chains.
</para>
<para>
When both of these options are set to <userinput>yes</userinput>
(the default) and a
query is being answered from authoritative data (a zone
configured into the server), the additional data section of
the
reply will be filled in using data from other authoritative
zones
and from the cache. In some situations this is undesirable,
such
as when there is concern over the correctness of the cache,
or
in servers where slave zones may be added and modified by
untrusted third parties. Also, avoiding
the search for this additional data will speed up server
operations
at the possible expense of additional queries to resolve
what would
otherwise be provided in the additional section.
</para>
<para>
For example, if a query asks for an MX record for host <literal>foo.example.com</literal>,
and the record found is "<literal>MX 10 mail.example.net</literal>", normally the address
records (A and AAAA) for <literal>mail.example.net</literal> will be provided as well,
if known, even though they are not in the example.com zone.
Setting these options to <command>no</command>
disables this behavior and makes
the server only search for additional data in the zone it
answers from.
</para>
<para>
These options are intended for use in authoritative-only
servers, or in authoritative-only views. Attempts to set
them to <command>no</command> without also
specifying
<command>recursion no</command> will cause the
server to
ignore the options and log a warning message.
</para>
<para>
Specifying <command>additional-from-cache no</command> actually
disables the use of the cache not only for additional data
lookups
but also when looking up the answer. This is usually the
desired
behavior in an authoritative-only server where the
correctness of
the cached data is an issue.
</para>
<para>
When a name server is non-recursively queried for a name
that is not
below the apex of any served zone, it normally answers with
an
"upwards referral" to the root servers or the servers of
some other
known parent of the query name. Since the data in an
upwards referral
comes from the cache, the server will not be able to provide
upwards
referrals when <command>additional-from-cache no</command>
has been specified. Instead, it will respond to such
queries
with REFUSED. This should not cause any problems since
upwards referrals are not required for the resolution
process.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>match-mapped-addresses</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, then an
IPv4-mapped IPv6 address will match any address match
list entries that match the corresponding IPv4 address.
</para>
<para>
This option was introduced to work around a kernel quirk
in some operating systems that causes IPv4 TCP
connections, such as zone transfers, to be accepted on an
IPv6 socket using mapped addresses. This caused address
match lists designed for IPv4 to fail to match. However,
<command>named</command> now solves this problem
internally. The use of this option is discouraged.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>filter-aaaa-on-v4</command></term>
<listitem>
<para>
This option is only available when
<acronym>BIND</acronym> 9 is compiled with the
<userinput>--enable-filter-aaaa</userinput> option on the
"configure" command line. It is intended to help the
transition from IPv4 to IPv6 by not giving IPv6 addresses
to DNS clients unless they have connections to the IPv6
Internet. This is not recommended unless absolutely
necessary. The default is <userinput>no</userinput>.
The <command>filter-aaaa-on-v4</command> option
may also be specified in <command>view</command> statements
to override the global <command>filter-aaaa-on-v4</command>
option.
</para>
<para>
If <userinput>yes</userinput>,
the DNS client is at an IPv4 address, in <command>filter-aaaa</command>,
and if the response does not include DNSSEC signatures,
then all AAAA records are deleted from the response.
This filtering applies to all responses and not only
authoritative responses.
</para>
<para>
If <userinput>break-dnssec</userinput>,
then AAAA records are deleted even when dnssec is enabled.
As suggested by the name, this makes the response not verify,
because the DNSSEC protocol is designed detect deletions.
</para>
<para>
This mechanism can erroneously cause other servers to
not give AAAA records to their clients.
A recursing server with both IPv6 and IPv4 network connections
that queries an authoritative server using this mechanism
via IPv4 will be denied AAAA records even if its client is
using IPv6.
</para>
<para>
This mechanism is applied to authoritative as well as
non-authoritative records.
A client using IPv4 that is not allowed recursion can
erroneously be given AAAA records because the server is not
allowed to check for A records.
</para>
<para>
Some AAAA records are given to IPv4 clients in glue records.
IPv4 clients that are servers can then erroneously
answer requests for AAAA records received via IPv4.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ixfr-from-differences</command></term>
<listitem>
<para>
When <userinput>yes</userinput> and the server loads a new version of a master
zone from its zone file or receives a new version of a slave
file by a non-incremental zone transfer, it will compare
the new version to the previous one and calculate a set
of differences. The differences are then logged in the
zone's journal file such that the changes can be transmitted
to downstream slaves as an incremental zone transfer.
</para>
<para>
By allowing incremental zone transfers to be used for
non-dynamic zones, this option saves bandwidth at the
expense of increased CPU and memory consumption at the
master.
In particular, if the new version of a zone is completely
different from the previous one, the set of differences
will be of a size comparable to the combined size of the
old and new zone version, and the server will need to
temporarily allocate memory to hold this complete
difference set.
</para>
<para><command>ixfr-from-differences</command>
also accepts <command>master</command> and
<command>slave</command> at the view and options
levels which causes
<command>ixfr-from-differences</command> to be enabled for
all <command>master</command> or
<command>slave</command> zones respectively.
It is off by default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>multi-master</command></term>
<listitem>
<para>
This should be set when you have multiple masters for a zone
and the
addresses refer to different machines. If <userinput>yes</userinput>, <command>named</command> will
not log
when the serial number on the master is less than what <command>named</command>
currently
has. The default is <userinput>no</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-enable</command></term>
<listitem>
<para>
Enable DNSSEC support in <command>named</command>. Unless set to <userinput>yes</userinput>,
<command>named</command> behaves as if it does not support DNSSEC.
The default is <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-validation</command></term>
<listitem>
<para>
Enable DNSSEC validation in <command>named</command>.
Note <command>dnssec-enable</command> also needs to be
set to <userinput>yes</userinput> to be effective.
If set to <userinput>no</userinput>, DNSSEC validation
is disabled. If set to <userinput>auto</userinput>,
DNSSEC validation is enabled, and a default
trust-anchor for the DNS root zone is used. If set to
<userinput>yes</userinput>, DNSSEC validation is enabled,
but a trust anchor must be manually configured using
a <command>trusted-keys</command> or
<command>managed-keys</command> statement. The default
is <userinput>yes</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-accept-expired</command></term>
<listitem>
<para>
Accept expired signatures when verifying DNSSEC signatures.
The default is <userinput>no</userinput>.
Setting this option to <userinput>yes</userinput>
leaves <command>named</command> vulnerable to
replay attacks.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>querylog</command></term>
<listitem>
<para>
Specify whether query logging should be started when <command>named</command>
starts.
If <command>querylog</command> is not specified,
then the query logging
is determined by the presence of the logging category <command>queries</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-names</command></term>
<listitem>
<para>
This option is used to restrict the character set and syntax
of
certain domain names in master files and/or DNS responses
received
from the network. The default varies according to usage
area. For
<command>master</command> zones the default is <command>fail</command>.
For <command>slave</command> zones the default
is <command>warn</command>.
For answers received from the network (<command>response</command>)
the default is <command>ignore</command>.
</para>
<para>
The rules for legal hostnames and mail domains are derived
from RFC 952 and RFC 821 as modified by RFC 1123.
</para>
<para><command>check-names</command>
applies to the owner names of A, AAAA and MX records.
It also applies to the domain names in the RDATA of NS, SOA,
MX, and SRV records.
It also applies to the RDATA of PTR records where the owner
name indicated that it is a reverse lookup of a hostname
(the owner name ends in IN-ADDR.ARPA, IP6.ARPA, or IP6.INT).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-dup-records</command></term>
<listitem>
<para>
Check master zones for records that are treated as different
by DNSSEC but are semantically equal in plain DNS. The
default is to <command>warn</command>. Other possible
values are <command>fail</command> and
<command>ignore</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-mx</command></term>
<listitem>
<para>
Check whether the MX record appears to refer to a IP address.
The default is to <command>warn</command>. Other possible
values are <command>fail</command> and
<command>ignore</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-wildcard</command></term>
<listitem>
<para>
This option is used to check for non-terminal wildcards.
The use of non-terminal wildcards is almost always as a
result of a failure
to understand the wildcard matching algorithm (RFC 1034).
This option
affects master zones. The default (<command>yes</command>) is to check
for non-terminal wildcards and issue a warning.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-integrity</command></term>
<listitem>
<para>
Perform post load zone integrity checks on master
zones. This checks that MX and SRV records refer
to address (A or AAAA) records and that glue
address records exist for delegated zones. For
MX and SRV records only in-zone hostnames are
checked (for out-of-zone hostnames use
<command>named-checkzone</command>).
For NS records only names below top of zone are
checked (for out-of-zone names and glue consistency
checks use <command>named-checkzone</command>).
The default is <command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-mx-cname</command></term>
<listitem>
<para>
If <command>check-integrity</command> is set then
fail, warn or ignore MX records that refer
to CNAMES. The default is to <command>warn</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-srv-cname</command></term>
<listitem>
<para>
If <command>check-integrity</command> is set then
fail, warn or ignore SRV records that refer
to CNAMES. The default is to <command>warn</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-sibling</command></term>
<listitem>
<para>
When performing integrity checks, also check that
sibling glue exists. The default is <command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zero-no-soa-ttl</command></term>
<listitem>
<para>
When returning authoritative negative responses to
SOA queries set the TTL of the SOA record returned in
the authority section to zero.
The default is <command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zero-no-soa-ttl-cache</command></term>
<listitem>
<para>
When caching a negative response to a SOA query
set the TTL to zero.
The default is <command>no</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>update-check-ksk</command></term>
<listitem>
<para>
When set to the default value of <literal>yes</literal>,
check the KSK bit in each key to determine how the key
should be used when generating RRSIGs for a secure zone.
</para>
<para>
Ordinarily, zone-signing keys (that is, keys without the
KSK bit set) are used to sign the entire zone, while
key-signing keys (keys with the KSK bit set) are only
used to sign the DNSKEY RRset at the zone apex.
However, if this option is set to <literal>no</literal>,
then the KSK bit is ignored; KSKs are treated as if they
were ZSKs and are used to sign the entire zone. This is
similar to the <command>dnssec-signzone -z</command>
command line option.
</para>
<para>
When this option is set to <literal>yes</literal>, there
must be at least two active keys for every algorithm
represented in the DNSKEY RRset: at least one KSK and one
ZSK per algorithm. If there is any algorithm for which
this requirement is not met, this option will be ignored
for that algorithm.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-dnskey-kskonly</command></term>
<listitem>
<para>
When this option and <command>update-check-ksk</command>
are both set to <literal>yes</literal>, only key-signing
keys (that is, keys with the KSK bit set) will be used
to sign the DNSKEY RRset at the zone apex. Zone-signing
keys (keys without the KSK bit set) will be used to sign
the remainder of the zone, but not the DNSKEY RRset.
This is similar to the
<command>dnssec-signzone -x</command> command line option.
</para>
<para>
The default is <command>no</command>. If
<command>update-check-ksk</command> is set to
<literal>no</literal>, this option is ignored.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>try-tcp-refresh</command></term>
<listitem>
<para>
Try to refresh the zone using TCP if UDP queries fail.
For BIND 8 compatibility, the default is
<command>yes</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-secure-to-insecure</command></term>
<listitem>
<para>
Allow a dynamic zone to transition from secure to
insecure (i.e., signed to unsigned) by deleting all
of the DNSKEY records. The default is <command>no</command>.
If set to <command>yes</command>, and if the DNSKEY RRset
at the zone apex is deleted, all RRSIG and NSEC records
will be removed from the zone as well.
</para>
<para>
If the zone uses NSEC3, then it is also necessary to
delete the NSEC3PARAM RRset from the zone apex; this will
cause the removal of all corresponding NSEC3 records.
(It is expected that this requirement will be eliminated
in a future release.)
</para>
<para>
Note that if a zone has been configured with
<command>auto-dnssec maintain</command> and the
private keys remain accessible in the key repository,
then the zone will be automatically signed again the
next time <command>named</command> is started.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3>
<title>Forwarding</title>
<para>
The forwarding facility can be used to create a large site-wide
cache on a few servers, reducing traffic over links to external
name servers. It can also be used to allow queries by servers that
do not have direct access to the Internet, but wish to look up
exterior
names anyway. Forwarding occurs only on those queries for which
the server is not authoritative and does not have the answer in
its cache.
</para>
<variablelist>
<varlistentry>
<term><command>forward</command></term>
<listitem>
<para>
This option is only meaningful if the
forwarders list is not empty. A value of <varname>first</varname>,
the default, causes the server to query the forwarders
first — and
if that doesn't answer the question, the server will then
look for
the answer itself. If <varname>only</varname> is
specified, the
server will only query the forwarders.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>forwarders</command></term>
<listitem>
<para>
Specifies the IP addresses to be used
for forwarding. The default is the empty list (no
forwarding).
</para>
</listitem>
</varlistentry>
</variablelist>
<para>
Forwarding can also be configured on a per-domain basis, allowing
for the global forwarding options to be overridden in a variety
of ways. You can set particular domains to use different
forwarders,
or have a different <command>forward only/first</command> behavior,
or not forward at all, see <xref linkend="zone_statement_grammar"/>.
</para>
</sect3>
<sect3>
<title>Dual-stack Servers</title>
<para>
Dual-stack servers are used as servers of last resort to work
around
problems in reachability due the lack of support for either IPv4
or IPv6
on the host machine.
</para>
<variablelist>
<varlistentry>
<term><command>dual-stack-servers</command></term>
<listitem>
<para>
Specifies host names or addresses of machines with access to
both IPv4 and IPv6 transports. If a hostname is used, the
server must be able
to resolve the name using only the transport it has. If the
machine is dual
stacked, then the <command>dual-stack-servers</command> have no effect unless
access to a transport has been disabled on the command line
(e.g. <command>named -4</command>).
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="access_control">
<title>Access Control</title>
<para>
Access to the server can be restricted based on the IP address
of the requesting system. See <xref linkend="address_match_lists"/> for
details on how to specify IP address lists.
</para>
<variablelist>
<varlistentry>
<term><command>allow-notify</command></term>
<listitem>
<para>
Specifies which hosts are allowed to
notify this server, a slave, of zone changes in addition
to the zone masters.
<command>allow-notify</command> may also be
specified in the
<command>zone</command> statement, in which case
it overrides the
<command>options allow-notify</command>
statement. It is only meaningful
for a slave zone. If not specified, the default is to
process notify messages
only from a zone's master.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query</command></term>
<listitem>
<para>
Specifies which hosts are allowed to ask ordinary
DNS questions. <command>allow-query</command> may
also be specified in the <command>zone</command>
statement, in which case it overrides the
<command>options allow-query</command> statement.
If not specified, the default is to allow queries
from all hosts.
</para>
<note>
<para>
<command>allow-query-cache</command> is now
used to specify access to the cache.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-on</command></term>
<listitem>
<para>
Specifies which local addresses can accept ordinary
DNS questions. This makes it possible, for instance,
to allow queries on internal-facing interfaces but
disallow them on external-facing ones, without
necessarily knowing the internal network's addresses.
</para>
<para>
<command>allow-query-on</command> may
also be specified in the <command>zone</command>
statement, in which case it overrides the
<command>options allow-query-on</command> statement.
</para>
<para>
If not specified, the default is to allow queries
on all addresses.
</para>
<note>
<para>
<command>allow-query-cache</command> is
used to specify access to the cache.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-cache</command></term>
<listitem>
<para>
Specifies which hosts are allowed to get answers
from the cache. If <command>allow-query-cache</command>
is not set then <command>allow-recursion</command>
is used if set, otherwise <command>allow-query</command>
is used if set unless <command>recursion no;</command> is
set in which case <command>none;</command> is used,
otherwise the default (<command>localnets;</command>
<command>localhost;</command>) is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-cache-on</command></term>
<listitem>
<para>
Specifies which local addresses can give answers
from the cache. If not specified, the default is
to allow cache queries on any address,
<command>localnets</command> and
<command>localhost</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-recursion</command></term>
<listitem>
<para>
Specifies which hosts are allowed to make recursive
queries through this server. If
<command>allow-recursion</command> is not set
then <command>allow-query-cache</command> is
used if set, otherwise <command>allow-query</command>
is used if set, otherwise the default
(<command>localnets;</command>
<command>localhost;</command>) is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-recursion-on</command></term>
<listitem>
<para>
Specifies which local addresses can accept recursive
queries. If not specified, the default is to allow
recursive queries on all addresses.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update</command></term>
<listitem>
<para>
Specifies which hosts are allowed to
submit Dynamic DNS updates for master zones. The default is
to deny
updates from all hosts. Note that allowing updates based
on the requestor's IP address is insecure; see
<xref linkend="dynamic_update_security"/> for details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update-forwarding</command></term>
<listitem>
<para>
Specifies which hosts are allowed to
submit Dynamic DNS updates to slave zones to be forwarded to
the
master. The default is <userinput>{ none; }</userinput>,
which
means that no update forwarding will be performed. To
enable
update forwarding, specify
<userinput>allow-update-forwarding { any; };</userinput>.
Specifying values other than <userinput>{ none; }</userinput> or
<userinput>{ any; }</userinput> is usually
counterproductive, since
the responsibility for update access control should rest
with the
master server, not the slaves.
</para>
<para>
Note that enabling the update forwarding feature on a slave
server
may expose master servers relying on insecure IP address
based
access control to attacks; see <xref linkend="dynamic_update_security"/>
for more details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-v6-synthesis</command></term>
<listitem>
<para>
This option was introduced for the smooth transition from
AAAA
to A6 and from "nibble labels" to binary labels.
However, since both A6 and binary labels were then
deprecated,
this option was also deprecated.
It is now ignored with some warning messages.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-transfer</command></term>
<listitem>
<para>
Specifies which hosts are allowed to
receive zone transfers from the server. <command>allow-transfer</command> may
also be specified in the <command>zone</command>
statement, in which
case it overrides the <command>options allow-transfer</command> statement.
If not specified, the default is to allow transfers to all
hosts.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>blackhole</command></term>
<listitem>
<para>
Specifies a list of addresses that the
server will not accept queries from or use to resolve a
query. Queries
from these addresses will not be responded to. The default
is <userinput>none</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>filter-aaaa</command></term>
<listitem>
<para>
Specifies a list of addresses to which
<command>filter-aaaa-on-v4</command>
is applies. The default is <userinput>any</userinput>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>resolver-query-timeout</command></term>
<listitem>
<para>
The amount of time the resolver will spend attempting
to resolve a recursive query before failing. The minimum
is <literal>10</literal> and the default and maximum is
<literal>30</literal>. Setting it to <literal>0</literal>
will result in the default being used.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3>
<title>Interfaces</title>
<para>
The interfaces and ports that the server will answer queries
from may be specified using the <command>listen-on</command> option. <command>listen-on</command> takes
an optional port and an <varname>address_match_list</varname>.
The server will listen on all interfaces allowed by the address
match list. If a port is not specified, port 53 will be used.
</para>
<para>
Multiple <command>listen-on</command> statements are
allowed.
For example,
</para>
<programlisting>listen-on { 5.6.7.8; };
listen-on port 1234 { !1.2.3.4; 1.2/16; };
</programlisting>
<para>
will enable the name server on port 53 for the IP address
5.6.7.8, and on port 1234 of an address on the machine in net
1.2 that is not 1.2.3.4.
</para>
<para>
If no <command>listen-on</command> is specified, the
server will listen on port 53 on all IPv4 interfaces.
</para>
<para>
The <command>listen-on-v6</command> option is used to
specify the interfaces and the ports on which the server will
listen
for incoming queries sent using IPv6.
</para>
<para>
When <programlisting>{ any; }</programlisting> is
specified
as the <varname>address_match_list</varname> for the
<command>listen-on-v6</command> option,
the server does not bind a separate socket to each IPv6 interface
address as it does for IPv4 if the operating system has enough API
support for IPv6 (specifically if it conforms to RFC 3493 and RFC
3542).
Instead, it listens on the IPv6 wildcard address.
If the system only has incomplete API support for IPv6, however,
the behavior is the same as that for IPv4.
</para>
<para>
A list of particular IPv6 addresses can also be specified, in
which case
the server listens on a separate socket for each specified
address,
regardless of whether the desired API is supported by the system.
</para>
<para>
Multiple <command>listen-on-v6</command> options can
be used.
For example,
</para>
<programlisting>listen-on-v6 { any; };
listen-on-v6 port 1234 { !2001:db8::/32; any; };
</programlisting>
<para>
will enable the name server on port 53 for any IPv6 addresses
(with a single wildcard socket),
and on port 1234 of IPv6 addresses that is not in the prefix
2001:db8::/32 (with separate sockets for each matched address.)
</para>
<para>
To make the server not listen on any IPv6 address, use
</para>
<programlisting>listen-on-v6 { none; };
</programlisting>
<para>
If no <command>listen-on-v6</command> option is
specified, the server will not listen on any IPv6 address
unless <command>-6</command> is specified when <command>named</command> is
invoked. If <command>-6</command> is specified then
<command>named</command> will listen on port 53 on all IPv6 interfaces by default.
</para>
</sect3>
<sect3 id="query_address">
<title>Query Address</title>
<para>
If the server doesn't know the answer to a question, it will
query other name servers. <command>query-source</command> specifies
the address and port used for such queries. For queries sent over
IPv6, there is a separate <command>query-source-v6</command> option.
If <command>address</command> is <command>*</command> (asterisk) or is omitted,
a wildcard IP address (<command>INADDR_ANY</command>)
will be used.
</para>
<para>
If <command>port</command> is <command>*</command> or is omitted,
a random port number from a pre-configured
range is picked up and will be used for each query.
The port range(s) is that specified in
the <command>use-v4-udp-ports</command> (for IPv4)
and <command>use-v6-udp-ports</command> (for IPv6)
options, excluding the ranges specified in
the <command>avoid-v4-udp-ports</command>
and <command>avoid-v6-udp-ports</command> options, respectively.
</para>
<para>
The defaults of the <command>query-source</command> and
<command>query-source-v6</command> options
are:
</para>
<programlisting>query-source address * port *;
query-source-v6 address * port *;
</programlisting>
<para>
If <command>use-v4-udp-ports</command> or
<command>use-v6-udp-ports</command> is unspecified,
<command>named</command> will check if the operating
system provides a programming interface to retrieve the
system's default range for ephemeral ports.
If such an interface is available,
<command>named</command> will use the corresponding system
default range; otherwise, it will use its own defaults:
</para>
<programlisting>use-v4-udp-ports { range 1024 65535; };
use-v6-udp-ports { range 1024 65535; };
</programlisting>
<para>
Note: make sure the ranges be sufficiently large for
security. A desirable size depends on various parameters,
but we generally recommend it contain at least 16384 ports
(14 bits of entropy).
Note also that the system's default range when used may be
too small for this purpose, and that the range may even be
changed while <command>named</command> is running; the new
range will automatically be applied when <command>named</command>
is reloaded.
It is encouraged to
configure <command>use-v4-udp-ports</command> and
<command>use-v6-udp-ports</command> explicitly so that the
ranges are sufficiently large and are reasonably
independent from the ranges used by other applications.
</para>
<para>
Note: the operational configuration
where <command>named</command> runs may prohibit the use
of some ports. For example, UNIX systems will not allow
<command>named</command> running without a root privilege
to use ports less than 1024.
If such ports are included in the specified (or detected)
set of query ports, the corresponding query attempts will
fail, resulting in resolution failures or delay.
It is therefore important to configure the set of ports
that can be safely used in the expected operational environment.
</para>
<para>
The defaults of the <command>avoid-v4-udp-ports</command> and
<command>avoid-v6-udp-ports</command> options
are:
</para>
<programlisting>avoid-v4-udp-ports {};
avoid-v6-udp-ports {};
</programlisting>
<para>
Note: BIND 9.5.0 introduced
the <command>use-queryport-pool</command>
option to support a pool of such random ports, but this
option is now obsolete because reusing the same ports in
the pool may not be sufficiently secure.
For the same reason, it is generally strongly discouraged to
specify a particular port for the
<command>query-source</command> or
<command>query-source-v6</command> options;
it implicitly disables the use of randomized port numbers.
</para>
<variablelist>
<varlistentry>
<term><command>use-queryport-pool</command></term>
<listitem>
<para>
This option is obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>queryport-pool-ports</command></term>
<listitem>
<para>
This option is obsolete.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>queryport-pool-updateinterval</command></term>
<listitem>
<para>
This option is obsolete.
</para>
</listitem>
</varlistentry>
</variablelist>
<note>
<para>
The address specified in the <command>query-source</command> option
is used for both UDP and TCP queries, but the port applies only
to UDP queries. TCP queries always use a random
unprivileged port.
</para>
</note>
<note>
<para>
Solaris 2.5.1 and earlier does not support setting the source
address for TCP sockets.
</para>
</note>
<note>
<para>
See also <command>transfer-source</command> and
<command>notify-source</command>.
</para>
</note>
</sect3>
<sect3 id="zone_transfers">
<title>Zone Transfers</title>
<para>
<acronym>BIND</acronym> has mechanisms in place to
facilitate zone transfers
and set limits on the amount of load that transfers place on the
system. The following options apply to zone transfers.
</para>
<variablelist>
<varlistentry>
<term><command>also-notify</command></term>
<listitem>
<para>
Defines a global list of IP addresses of name servers
that are also sent NOTIFY messages whenever a fresh copy of
the
zone is loaded, in addition to the servers listed in the
zone's NS records.
This helps to ensure that copies of the zones will
quickly converge on stealth servers.
Optionally, a port may be specified with each
<command>also-notify</command> address to send
the notify messages to a port other than the
default of 53.
If an <command>also-notify</command> list
is given in a <command>zone</command> statement,
it will override
the <command>options also-notify</command>
statement. When a <command>zone notify</command>
statement
is set to <command>no</command>, the IP
addresses in the global <command>also-notify</command> list will
not be sent NOTIFY messages for that zone. The default is
the empty
list (no global notification list).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-in</command></term>
<listitem>
<para>
Inbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-in</command></term>
<listitem>
<para>
Inbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes
(1 hour). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-out</command></term>
<listitem>
<para>
Outbound zone transfers running longer than
this many minutes will be terminated. The default is 120
minutes
(2 hours). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-out</command></term>
<listitem>
<para>
Outbound zone transfers making no progress
in this many minutes will be terminated. The default is 60
minutes (1
hour). The maximum value is 28 days (40320 minutes).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>serial-query-rate</command></term>
<listitem>
<para>
Slave servers will periodically query master
servers to find out if zone serial numbers have
changed. Each such query uses a minute amount of
the slave server's network bandwidth. To limit
the amount of bandwidth used, BIND 9 limits the
rate at which queries are sent. The value of the
<command>serial-query-rate</command> option, an
integer, is the maximum number of queries sent
per second. The default is 20.
</para>
<para>
In addition to controlling the rate SOA refresh
queries are issued at
<command>serial-query-rate</command> also controls
the rate at which NOTIFY messages are sent from
both master and slave zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>serial-queries</command></term>
<listitem>
<para>
In BIND 8, the <command>serial-queries</command>
option
set the maximum number of concurrent serial number queries
allowed to be outstanding at any given time.
BIND 9 does not limit the number of outstanding
serial queries and ignores the <command>serial-queries</command> option.
Instead, it limits the rate at which the queries are sent
as defined using the <command>serial-query-rate</command> option.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-format</command></term>
<listitem>
<para>
Zone transfers can be sent using two different formats,
<command>one-answer</command> and
<command>many-answers</command>.
The <command>transfer-format</command> option is used
on the master server to determine which format it sends.
<command>one-answer</command> uses one DNS message per
resource record transferred.
<command>many-answers</command> packs as many resource
records as possible into a message.
<command>many-answers</command> is more efficient, but is
only supported by relatively new slave servers,
such as <acronym>BIND</acronym> 9, <acronym>BIND</acronym>
8.x and <acronym>BIND</acronym> 4.9.5 onwards.
The <command>many-answers</command> format is also supported by
recent Microsoft Windows nameservers.
The default is <command>many-answers</command>.
<command>transfer-format</command> may be overridden on a
per-server basis by using the <command>server</command>
statement.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfers-in</command></term>
<listitem>
<para>
The maximum number of inbound zone transfers
that can be running concurrently. The default value is <literal>10</literal>.
Increasing <command>transfers-in</command> may
speed up the convergence
of slave zones, but it also may increase the load on the
local system.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfers-out</command></term>
<listitem>
<para>
The maximum number of outbound zone transfers
that can be running concurrently. Zone transfer requests in
excess
of the limit will be refused. The default value is <literal>10</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfers-per-ns</command></term>
<listitem>
<para>
The maximum number of inbound zone transfers
that can be concurrently transferring from a given remote
name server.
The default value is <literal>2</literal>.
Increasing <command>transfers-per-ns</command>
may
speed up the convergence of slave zones, but it also may
increase
the load on the remote name server. <command>transfers-per-ns</command> may
be overridden on a per-server basis by using the <command>transfers</command> phrase
of the <command>server</command> statement.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source</command></term>
<listitem>
<para><command>transfer-source</command>
determines which local address will be bound to IPv4
TCP connections used to fetch zones transferred
inbound by the server. It also determines the
source IPv4 address, and optionally the UDP port,
used for the refresh queries and forwarded dynamic
updates. If not set, it defaults to a system
controlled value which will usually be the address
of the interface "closest to" the remote end. This
address must appear in the remote end's
<command>allow-transfer</command> option for the
zone being transferred, if one is specified. This
statement sets the
<command>transfer-source</command> for all zones,
but can be overridden on a per-view or per-zone
basis by including a
<command>transfer-source</command> statement within
the <command>view</command> or
<command>zone</command> block in the configuration
file.
</para>
<note>
<para>
Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source-v6</command></term>
<listitem>
<para>
The same as <command>transfer-source</command>,
except zone transfers are performed using IPv6.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source</command></term>
<listitem>
<para>
An alternate transfer source if the one listed in
<command>transfer-source</command> fails and
<command>use-alt-transfer-source</command> is
set.
</para>
<note>
If you do not wish the alternate transfer source
to be used, you should set
<command>use-alt-transfer-source</command>
appropriately and you should not depend upon
getting an answer back to the first refresh
query.
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source-v6</command></term>
<listitem>
<para>
An alternate transfer source if the one listed in
<command>transfer-source-v6</command> fails and
<command>use-alt-transfer-source</command> is
set.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-alt-transfer-source</command></term>
<listitem>
<para>
Use the alternate transfer sources or not. If views are
specified this defaults to <command>no</command>
otherwise it defaults to
<command>yes</command> (for BIND 8
compatibility).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source</command></term>
<listitem>
<para><command>notify-source</command>
determines which local source address, and
optionally UDP port, will be used to send NOTIFY
messages. This address must appear in the slave
server's <command>masters</command> zone clause or
in an <command>allow-notify</command> clause. This
statement sets the <command>notify-source</command>
for all zones, but can be overridden on a per-zone or
per-view basis by including a
<command>notify-source</command> statement within
the <command>zone</command> or
<command>view</command> block in the configuration
file.
</para>
<note>
<para>
Solaris 2.5.1 and earlier does not support setting the
source address for TCP sockets.
</para>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source-v6</command></term>
<listitem>
<para>
Like <command>notify-source</command>,
but applies to notify messages sent to IPv6 addresses.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3>
<title>UDP Port Lists</title>
<para>
<command>use-v4-udp-ports</command>,
<command>avoid-v4-udp-ports</command>,
<command>use-v6-udp-ports</command>, and
<command>avoid-v6-udp-ports</command>
specify a list of IPv4 and IPv6 UDP ports that will be
used or not used as source ports for UDP messages.
See <xref linkend="query_address"/> about how the
available ports are determined.
For example, with the following configuration
</para>
<programlisting>
use-v6-udp-ports { range 32768 65535; };
avoid-v6-udp-ports { 40000; range 50000 60000; };
</programlisting>
<para>
UDP ports of IPv6 messages sent
from <command>named</command> will be in one
of the following ranges: 32768 to 39999, 40001 to 49999,
and 60001 to 65535.
</para>
<para>
<command>avoid-v4-udp-ports</command> and
<command>avoid-v6-udp-ports</command> can be used
to prevent <command>named</command> from choosing as its random source port a
port that is blocked by your firewall or a port that is
used by other applications;
if a query went out with a source port blocked by a
firewall, the
answer would not get by the firewall and the name server would
have to query again.
Note: the desired range can also be represented only with
<command>use-v4-udp-ports</command> and
<command>use-v6-udp-ports</command>, and the
<command>avoid-</command> options are redundant in that
sense; they are provided for backward compatibility and
to possibly simplify the port specification.
</para>
</sect3>
<sect3>
<title>Operating System Resource Limits</title>
<para>
The server's usage of many system resources can be limited.
Scaled values are allowed when specifying resource limits. For
example, <command>1G</command> can be used instead of
<command>1073741824</command> to specify a limit of
one
gigabyte. <command>unlimited</command> requests
unlimited use, or the
maximum available amount. <command>default</command>
uses the limit
that was in force when the server was started. See the description
of <command>size_spec</command> in <xref linkend="configuration_file_elements"/>.
</para>
<para>
The following options set operating system resource limits for
the name server process. Some operating systems don't support
some or
any of the limits. On such systems, a warning will be issued if
the
unsupported limit is used.
</para>
<variablelist>
<varlistentry>
<term><command>coresize</command></term>
<listitem>
<para>
The maximum size of a core dump. The default
is <literal>default</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>datasize</command></term>
<listitem>
<para>
The maximum amount of data memory the server
may use. The default is <literal>default</literal>.
This is a hard limit on server memory usage.
If the server attempts to allocate memory in excess of this
limit, the allocation will fail, which may in turn leave
the server unable to perform DNS service. Therefore,
this option is rarely useful as a way of limiting the
amount of memory used by the server, but it can be used
to raise an operating system data size limit that is
too small by default. If you wish to limit the amount
of memory used by the server, use the
<command>max-cache-size</command> and
<command>recursive-clients</command>
options instead.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>files</command></term>
<listitem>
<para>
The maximum number of files the server
may have open concurrently. The default is <literal>unlimited</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>stacksize</command></term>
<listitem>
<para>
The maximum amount of stack memory the server
may use. The default is <literal>default</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="server_resource_limits">
<title>Server Resource Limits</title>
<para>
The following options set limits on the server's
resource consumption that are enforced internally by the
server rather than the operating system.
</para>
<variablelist>
<varlistentry>
<term><command>max-ixfr-log-size</command></term>
<listitem>
<para>
This option is obsolete; it is accepted
and ignored for BIND 8 compatibility. The option
<command>max-journal-size</command> performs a
similar function in BIND 9.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-journal-size</command></term>
<listitem>
<para>
Sets a maximum size for each journal file
(see <xref linkend="journal"/>). When the journal file
approaches
the specified size, some of the oldest transactions in the
journal
will be automatically removed. The default is
<literal>unlimited</literal>.
This may also be set on a per-zone basis.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>host-statistics-max</command></term>
<listitem>
<para>
In BIND 8, specifies the maximum number of host statistics
entries to be kept.
Not implemented in BIND 9.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>recursive-clients</command></term>
<listitem>
<para>
The maximum number of simultaneous recursive lookups
the server will perform on behalf of clients. The default
is
<literal>1000</literal>. Because each recursing
client uses a fair
bit of memory, on the order of 20 kilobytes, the value of
the
<command>recursive-clients</command> option may
have to be decreased
on hosts with limited memory.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-clients</command></term>
<listitem>
<para>
The maximum number of simultaneous client TCP
connections that the server will accept.
The default is <literal>100</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>reserved-sockets</command></term>
<listitem>
<para>
The number of file descriptors reserved for TCP, stdio,
etc. This needs to be big enough to cover the number of
interfaces <command>named</command> listens on plus
<command>tcp-clients</command>, as well as
to provide room for outgoing TCP queries and incoming zone
transfers. The default is <literal>512</literal>.
The minimum value is <literal>128</literal> and the
maximum value is <literal>128</literal> less than
maxsockets (-S). This option may be removed in the future.
</para>
<para>
This option has little effect on Windows.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-cache-size</command></term>
<listitem>
<para>
The maximum amount of memory to use for the
server's cache, in bytes.
When the amount of data in the cache
reaches this limit, the server will cause records to expire
prematurely based on an LRU based strategy so that
the limit is not exceeded.
A value of 0 is special, meaning that
records are purged from the cache only when their
TTLs expire.
Another special keyword <userinput>unlimited</userinput>
means the maximum value of 32-bit unsigned integers
(0xffffffff), which may not have the same effect as
0 on machines that support more than 32 bits of
memory space.
Any positive values less than 2MB will be ignored reset
to 2MB.
In a server with multiple views, the limit applies
separately to the cache of each view.
The default is 0.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>tcp-listen-queue</command></term>
<listitem>
<para>
The listen queue depth. The default and minimum is 3.
If the kernel supports the accept filter "dataready" this
also controls how
many TCP connections that will be queued in kernel space
waiting for
some data before being passed to accept. Values less than 3
will be
silently raised.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3>
<title>Periodic Task Intervals</title>
<variablelist>
<varlistentry>
<term><command>cleaning-interval</command></term>
<listitem>
<para>
This interval is effectively obsolete. Previously,
the server would remove expired resource records
from the cache every <command>cleaning-interval</command> minutes.
<acronym>BIND</acronym> 9 now manages cache
memory in a more sophisticated manner and does not
rely on the periodic cleaning any more.
Specifying this option therefore has no effect on
the server's behavior.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>heartbeat-interval</command></term>
<listitem>
<para>
The server will perform zone maintenance tasks
for all zones marked as <command>dialup</command> whenever this
interval expires. The default is 60 minutes. Reasonable
values are up
to 1 day (1440 minutes). The maximum value is 28 days
(40320 minutes).
If set to 0, no zone maintenance for these zones will occur.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>interface-interval</command></term>
<listitem>
<para>
The server will scan the network interface list
every <command>interface-interval</command>
minutes. The default
is 60 minutes. The maximum value is 28 days (40320 minutes).
If set to 0, interface scanning will only occur when
the configuration file is loaded. After the scan, the
server will
begin listening for queries on any newly discovered
interfaces (provided they are allowed by the
<command>listen-on</command> configuration), and
will
stop listening on interfaces that have gone away.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>statistics-interval</command></term>
<listitem>
<para>
Name server statistics will be logged
every <command>statistics-interval</command>
minutes. The default is
60. The maximum value is 28 days (40320 minutes).
If set to 0, no statistics will be logged.
</para><note>
<simpara>
Not yet implemented in
<acronym>BIND</acronym> 9.
</simpara>
</note>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="topology">
<title>Topology</title>
<para>
All other things being equal, when the server chooses a name
server
to query from a list of name servers, it prefers the one that is
topologically closest to itself. The <command>topology</command> statement
takes an <command>address_match_list</command> and
interprets it
in a special way. Each top-level list element is assigned a
distance.
Non-negated elements get a distance based on their position in the
list, where the closer the match is to the start of the list, the
shorter the distance is between it and the server. A negated match
will be assigned the maximum distance from the server. If there
is no match, the address will get a distance which is further than
any non-negated list element, and closer than any negated element.
For example,
</para>
<programlisting>topology {
10/8;
!1.2.3/24;
{ 1.2/16; 3/8; };
};</programlisting>
<para>
will prefer servers on network 10 the most, followed by hosts
on network 1.2.0.0 (netmask 255.255.0.0) and network 3, with the
exception of hosts on network 1.2.3 (netmask 255.255.255.0), which
is preferred least of all.
</para>
<para>
The default topology is
</para>
<programlisting> topology { localhost; localnets; };
</programlisting>
<note>
<simpara>
The <command>topology</command> option
is not implemented in <acronym>BIND</acronym> 9.
</simpara>
</note>
</sect3>
<sect3 id="the_sortlist_statement">
<title>The <command>sortlist</command> Statement</title>
<para>
The response to a DNS query may consist of multiple resource
records (RRs) forming a resource records set (RRset).
The name server will normally return the
RRs within the RRset in an indeterminate order
(but see the <command>rrset-order</command>
statement in <xref linkend="rrset_ordering"/>).
The client resolver code should rearrange the RRs as appropriate,
that is, using any addresses on the local net in preference to
other addresses.
However, not all resolvers can do this or are correctly
configured.
When a client is using a local server, the sorting can be performed
in the server, based on the client's address. This only requires
configuring the name servers, not all the clients.
</para>
<para>
The <command>sortlist</command> statement (see below)
takes
an <command>address_match_list</command> and
interprets it even
more specifically than the <command>topology</command>
statement
does (<xref linkend="topology"/>).
Each top level statement in the <command>sortlist</command> must
itself be an explicit <command>address_match_list</command> with
one or two elements. The first element (which may be an IP
address,
an IP prefix, an ACL name or a nested <command>address_match_list</command>)
of each top level list is checked against the source address of
the query until a match is found.
</para>
<para>
Once the source address of the query has been matched, if
the top level statement contains only one element, the actual
primitive
element that matched the source address is used to select the
address
in the response to move to the beginning of the response. If the
statement is a list of two elements, then the second element is
treated the same as the <command>address_match_list</command> in
a <command>topology</command> statement. Each top
level element
is assigned a distance and the address in the response with the
minimum
distance is moved to the beginning of the response.
</para>
<para>
In the following example, any queries received from any of
the addresses of the host itself will get responses preferring
addresses
on any of the locally connected networks. Next most preferred are
addresses
on the 192.168.1/24 network, and after that either the
192.168.2/24
or
192.168.3/24 network with no preference shown between these two
networks. Queries received from a host on the 192.168.1/24 network
will prefer other addresses on that network to the 192.168.2/24
and
192.168.3/24 networks. Queries received from a host on the
192.168.4/24
or the 192.168.5/24 network will only prefer other addresses on
their directly connected networks.
</para>
<programlisting>sortlist {
// IF the local host
// THEN first fit on the following nets
{ localhost;
{ localnets;
192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.1 THEN use .1, or .2 or .3
{ 192.168.1/24;
{ 192.168.1/24;
{ 192.168.2/24; 192.168.3/24; }; }; };
// IF on class C 192.168.2 THEN use .2, or .1 or .3
{ 192.168.2/24;
{ 192.168.2/24;
{ 192.168.1/24; 192.168.3/24; }; }; };
// IF on class C 192.168.3 THEN use .3, or .1 or .2
{ 192.168.3/24;
{ 192.168.3/24;
{ 192.168.1/24; 192.168.2/24; }; }; };
// IF .4 or .5 THEN prefer that net
{ { 192.168.4/24; 192.168.5/24; };
};
};</programlisting>
<para>
The following example will give reasonable behavior for the
local host and hosts on directly connected networks. It is similar
to the behavior of the address sort in <acronym>BIND</acronym> 4.9.x. Responses sent
to queries from the local host will favor any of the directly
connected
networks. Responses sent to queries from any other hosts on a
directly
connected network will prefer addresses on that same network.
Responses
to other queries will not be sorted.
</para>
<programlisting>sortlist {
{ localhost; localnets; };
{ localnets; };
};
</programlisting>
</sect3>
<sect3 id="rrset_ordering">
<title id="rrset_ordering_title">RRset Ordering</title>
<para>
When multiple records are returned in an answer it may be
useful to configure the order of the records placed into the
response.
The <command>rrset-order</command> statement permits
configuration
of the ordering of the records in a multiple record response.
See also the <command>sortlist</command> statement,
<xref linkend="the_sortlist_statement"/>.
</para>
<para>
An <command>order_spec</command> is defined as
follows:
</para>
<para>
<optional>class <replaceable>class_name</replaceable></optional>
<optional>type <replaceable>type_name</replaceable></optional>
<optional>name <replaceable>"domain_name"</replaceable></optional>
order <replaceable>ordering</replaceable>
</para>
<para>
If no class is specified, the default is <command>ANY</command>.
If no type is specified, the default is <command>ANY</command>.
If no name is specified, the default is "<command>*</command>" (asterisk).
</para>
<para>
The legal values for <command>ordering</command> are:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.750in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.750in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>fixed</command></para>
</entry>
<entry colname="2">
<para>
Records are returned in the order they
are defined in the zone file.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>random</command></para>
</entry>
<entry colname="2">
<para>
Records are returned in some random order.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>cyclic</command></para>
</entry>
<entry colname="2">
<para>
Records are returned in a cyclic round-robin order.
</para>
<para>
If <acronym>BIND</acronym> is configured with the
"--enable-fixed-rrset" option at compile time, then
the initial ordering of the RRset will match the
one specified in the zone file.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
For example:
</para>
<programlisting>rrset-order {
class IN type A name "host.example.com" order random;
order cyclic;
};
</programlisting>
<para>
will cause any responses for type A records in class IN that
have "<literal>host.example.com</literal>" as a
suffix, to always be returned
in random order. All other records are returned in cyclic order.
</para>
<para>
If multiple <command>rrset-order</command> statements
appear,
they are not combined — the last one applies.
</para>
<note>
<simpara>
In this release of <acronym>BIND</acronym> 9, the
<command>rrset-order</command> statement does not support
"fixed" ordering by default. Fixed ordering can be enabled
at compile time by specifying "--enable-fixed-rrset" on
the "configure" command line.
</simpara>
</note>
</sect3>
<sect3 id="tuning">
<title>Tuning</title>
<variablelist>
<varlistentry>
<term><command>lame-ttl</command></term>
<listitem>
<para>
Sets the number of seconds to cache a
lame server indication. 0 disables caching. (This is
<emphasis role="bold">NOT</emphasis> recommended.)
The default is <literal>600</literal> (10 minutes) and the
maximum value is
<literal>1800</literal> (30 minutes).
</para>
<para>
Lame-ttl also controls the amount of time DNSSEC
validation failures are cached. There is a minimum
of 30 seconds applied to bad cache entries if the
lame-ttl is set to less than 30 seconds.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-ncache-ttl</command></term>
<listitem>
<para>
To reduce network traffic and increase performance,
the server stores negative answers. <command>max-ncache-ttl</command> is
used to set a maximum retention time for these answers in
the server
in seconds. The default
<command>max-ncache-ttl</command> is <literal>10800</literal> seconds (3 hours).
<command>max-ncache-ttl</command> cannot exceed
7 days and will
be silently truncated to 7 days if set to a greater value.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-cache-ttl</command></term>
<listitem>
<para>
Sets the maximum time for which the server will
cache ordinary (positive) answers. The default is
one week (7 days).
A value of zero may cause all queries to return
SERVFAIL, because of lost caches of intermediate
RRsets (such as NS and glue AAAA/A records) in the
resolution process.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-roots</command></term>
<listitem>
<para>
The minimum number of root servers that
is required for a request for the root servers to be
accepted. The default
is <userinput>2</userinput>.
</para>
<note>
<simpara>
Not implemented in <acronym>BIND</acronym> 9.
</simpara>
</note>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-validity-interval</command></term>
<listitem>
<para>
Specifies the number of days into the future when
DNSSEC signatures automatically generated as a
result of dynamic updates (<xref
linkend="dynamic_update"/>) will expire. There
is an optional second field which specifies how
long before expiry that the signatures will be
regenerated. If not specified, the signatures will
be regenerated at 1/4 of base interval. The second
field is specified in days if the base interval is
greater than 7 days otherwise it is specified in hours.
The default base interval is <literal>30</literal> days
giving a re-signing interval of 7 1/2 days. The maximum
values are 10 years (3660 days).
</para>
<para>
The signature inception time is unconditionally
set to one hour before the current time to allow
for a limited amount of clock skew.
</para>
<para>
The <command>sig-validity-interval</command>
should be, at least, several multiples of the SOA
expire interval to allow for reasonable interaction
between the various timer and expiry dates.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-nodes</command></term>
<listitem>
<para>
Specify the maximum number of nodes to be
examined in each quantum when signing a zone with
a new DNSKEY. The default is
<literal>100</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-signatures</command></term>
<listitem>
<para>
Specify a threshold number of signatures that
will terminate processing a quantum when signing
a zone with a new DNSKEY. The default is
<literal>10</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-type</command></term>
<listitem>
<para>
Specify a private RDATA type to be used when generating
key signing records. The default is
<literal>65534</literal>.
</para>
<para>
It is expected that this parameter may be removed
in a future version once there is a standard type.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-refresh-time</command></term>
<term><command>max-refresh-time</command></term>
<term><command>min-retry-time</command></term>
<term><command>max-retry-time</command></term>
<listitem>
<para>
These options control the server's behavior on refreshing a
zone
(querying for SOA changes) or retrying failed transfers.
Usually the SOA values for the zone are used, but these
values
are set by the master, giving slave server administrators
little
control over their contents.
</para>
<para>
These options allow the administrator to set a minimum and
maximum
refresh and retry time either per-zone, per-view, or
globally.
These options are valid for slave and stub zones,
and clamp the SOA refresh and retry times to the specified
values.
</para>
<para>
The following defaults apply.
<command>min-refresh-time</command> 300 seconds,
<command>max-refresh-time</command> 2419200 seconds
(4 weeks), <command>min-retry-time</command> 500 seconds,
and <command>max-retry-time</command> 1209600 seconds
(2 weeks).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>edns-udp-size</command></term>
<listitem>
<para>
Sets the advertised EDNS UDP buffer size in bytes
to control the size of packets received.
Valid values are 512 to 4096 (values outside this range
will be silently adjusted). The default value
is 4096. The usual reason for setting
<command>edns-udp-size</command> to a non-default
value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.
</para>
<para>
<command>named</command> will fallback to using 512 bytes
if it get a series of timeout at the initial value. 512
bytes is not being offered to encourage sites to fix their
firewalls. Small EDNS UDP sizes will result in the
excessive use of TCP.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-udp-size</command></term>
<listitem>
<para>
Sets the maximum EDNS UDP message size
<command>named</command> will send in bytes.
Valid values are 512 to 4096 (values outside this
range will be silently adjusted). The default
value is 4096. The usual reason for setting
<command>max-udp-size</command> to a non-default
value is to get UDP answers to pass through broken
firewalls that block fragmented packets and/or
block UDP packets that are greater than 512 bytes.
This is independent of the advertised receive
buffer (<command>edns-udp-size</command>).
</para>
<para>
Setting this to a low value will encourage additional
TCP traffic to the nameserver.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>masterfile-format</command></term>
<listitem>
<para>Specifies
the file format of zone files (see
<xref linkend="zonefile_format"/>).
The default value is <constant>text</constant>, which is the
standard textual representation. Files in other formats
than <constant>text</constant> are typically expected
to be generated by the <command>named-compilezone</command> tool.
Note that when a zone file in a different format than
<constant>text</constant> is loaded, <command>named</command>
may omit some of the checks which would be performed for a
file in the <constant>text</constant> format. In particular,
<command>check-names</command> checks do not apply
for the <constant>raw</constant> format. This means
a zone file in the <constant>raw</constant> format
must be generated with the same check level as that
specified in the <command>named</command> configuration
file. This statement sets the
<command>masterfile-format</command> for all zones,
but can be overridden on a per-zone or per-view basis
by including a <command>masterfile-format</command>
statement within the <command>zone</command> or
<command>view</command> block in the configuration
file.
</para>
</listitem>
</varlistentry>
<varlistentry id="clients-per-query">
<term><command>clients-per-query</command></term>
<term><command>max-clients-per-query</command></term>
<listitem>
<para>These set the
initial value (minimum) and maximum number of recursive
simultaneous clients for any given query
(<qname,qtype,qclass>) that the server will accept
before dropping additional clients. <command>named</command> will attempt to
self tune this value and changes will be logged. The
default values are 10 and 100.
</para>
<para>
This value should reflect how many queries come in for
a given name in the time it takes to resolve that name.
If the number of queries exceed this value, <command>named</command> will
assume that it is dealing with a non-responsive zone
and will drop additional queries. If it gets a response
after dropping queries, it will raise the estimate. The
estimate will then be lowered in 20 minutes if it has
remained unchanged.
</para>
<para>
If <command>clients-per-query</command> is set to zero,
then there is no limit on the number of clients per query
and no queries will be dropped.
</para>
<para>
If <command>max-clients-per-query</command> is set to zero,
then there is no upper bound other than imposed by
<command>recursive-clients</command>.
</para>
</listitem>
</varlistentry>
<varlistentry id="max-recursion-depth">
<term><command>max-recursion-depth</command></term>
<listitem>
<para>
Sets the maximum number of levels of recursion
that are permitted at any one time while servicing
a recursive query. Resolving a name may require
looking up a name server address, which in turn
requires resolving another name, etc; if the number
of indirections exceeds this value, the recursive
query is terminated and returns SERVFAIL. The
default is 7.
</para>
</listitem>
</varlistentry>
<varlistentry id="max-recursion-queries">
<term><command>max-recursion-queries</command></term>
<listitem>
<para>
Sets the maximum number of iterative queries that
may be sent while servicing a recursive query.
If more queries are sent, the recursive query
is terminated and returns SERVFAIL. The default
is 50.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-delay</command></term>
<listitem>
<para>
The delay, in seconds, between sending sets of notify
messages for a zone. The default is five (5) seconds.
</para>
<para>
The overall rate that NOTIFY messages are sent for all
zones is controlled by <command>serial-query-rate</command>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="builtin">
<title>Built-in server information zones</title>
<para>
The server provides some helpful diagnostic information
through a number of built-in zones under the
pseudo-top-level-domain <literal>bind</literal> in the
<command>CHAOS</command> class. These zones are part
of a
built-in view (see <xref linkend="view_statement_grammar"/>) of
class
<command>CHAOS</command> which is separate from the
default view of
class <command>IN</command>; therefore, any global
server options
such as <command>allow-query</command> do not apply
the these zones.
If you feel the need to disable these zones, use the options
below, or hide the built-in <command>CHAOS</command>
view by
defining an explicit view of class <command>CHAOS</command>
that matches all clients.
</para>
<variablelist>
<varlistentry>
<term><command>version</command></term>
<listitem>
<para>
The version the server should report
via a query of the name <literal>version.bind</literal>
with type <command>TXT</command>, class <command>CHAOS</command>.
The default is the real version number of this server.
Specifying <command>version none</command>
disables processing of the queries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>hostname</command></term>
<listitem>
<para>
The hostname the server should report via a query of
the name <filename>hostname.bind</filename>
with type <command>TXT</command>, class <command>CHAOS</command>.
This defaults to the hostname of the machine hosting the
name server as
found by the gethostname() function. The primary purpose of such queries
is to
identify which of a group of anycast servers is actually
answering your queries. Specifying <command>hostname none;</command>
disables processing of the queries.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>server-id</command></term>
<listitem>
<para>
The ID the server should report when receiving a Name
Server Identifier (NSID) query, or a query of the name
<filename>ID.SERVER</filename> with type
<command>TXT</command>, class <command>CHAOS</command>.
The primary purpose of such queries is to
identify which of a group of anycast servers is actually
answering your queries. Specifying <command>server-id none;</command>
disables processing of the queries.
Specifying <command>server-id hostname;</command> will cause <command>named</command> to
use the hostname as found by the gethostname() function.
The default <command>server-id</command> is <command>none</command>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="empty">
<title>Built-in Empty Zones</title>
<para>
Named has some built-in empty zones (SOA and NS records only).
These are for zones that should normally be answered locally
and which queries should not be sent to the Internet's root
servers. The official servers which cover these namespaces
return NXDOMAIN responses to these queries. In particular,
these cover the reverse namespaces for addresses from
RFC 1918, RFC 4193, and RFC 5737. They also include the
reverse namespace for IPv6 local address (locally assigned),
IPv6 link local addresses, the IPv6 loopback address and the
IPv6 unknown address.
</para>
<para>
Named will attempt to determine if a built-in zone already exists
or is active (covered by a forward-only forwarding declaration)
and will not create an empty zone in that case.
</para>
<para>
The current list of empty zones is:
<itemizedlist>
<listitem>10.IN-ADDR.ARPA</listitem>
<listitem>16.172.IN-ADDR.ARPA</listitem>
<listitem>17.172.IN-ADDR.ARPA</listitem>
<listitem>18.172.IN-ADDR.ARPA</listitem>
<listitem>19.172.IN-ADDR.ARPA</listitem>
<listitem>20.172.IN-ADDR.ARPA</listitem>
<listitem>21.172.IN-ADDR.ARPA</listitem>
<listitem>22.172.IN-ADDR.ARPA</listitem>
<listitem>23.172.IN-ADDR.ARPA</listitem>
<listitem>24.172.IN-ADDR.ARPA</listitem>
<listitem>25.172.IN-ADDR.ARPA</listitem>
<listitem>26.172.IN-ADDR.ARPA</listitem>
<listitem>27.172.IN-ADDR.ARPA</listitem>
<listitem>28.172.IN-ADDR.ARPA</listitem>
<listitem>29.172.IN-ADDR.ARPA</listitem>
<listitem>30.172.IN-ADDR.ARPA</listitem>
<listitem>31.172.IN-ADDR.ARPA</listitem>
<listitem>168.192.IN-ADDR.ARPA</listitem>
<listitem>0.IN-ADDR.ARPA</listitem>
<listitem>127.IN-ADDR.ARPA</listitem>
<listitem>254.169.IN-ADDR.ARPA</listitem>
<listitem>2.0.192.IN-ADDR.ARPA</listitem>
<listitem>100.51.198.IN-ADDR.ARPA</listitem>
<listitem>113.0.203.IN-ADDR.ARPA</listitem>
<listitem>255.255.255.255.IN-ADDR.ARPA</listitem>
<listitem>0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</listitem>
<listitem>1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.IP6.ARPA</listitem>
<listitem>8.B.D.0.1.0.0.2.IP6.ARPA</listitem>
<listitem>D.F.IP6.ARPA</listitem>
<listitem>8.E.F.IP6.ARPA</listitem>
<listitem>9.E.F.IP6.ARPA</listitem>
<listitem>A.E.F.IP6.ARPA</listitem>
<listitem>B.E.F.IP6.ARPA</listitem>
</itemizedlist>
</para>
<para>
Empty zones are settable at the view level and only apply to
views of class IN. Disabled empty zones are only inherited
from options if there are no disabled empty zones specified
at the view level. To override the options list of disabled
zones, you can disable the root zone at the view level, for example:
<programlisting>
disable-empty-zone ".";
</programlisting>
</para>
<para>
If you are using the address ranges covered here, you should
already have reverse zones covering the addresses you use.
In practice this appears to not be the case with many queries
being made to the infrastructure servers for names in these
spaces. So many in fact that sacrificial servers were needed
to be deployed to channel the query load away from the
infrastructure servers.
</para>
<note>
The real parent servers for these zones should disable all
empty zone under the parent zone they serve. For the real
root servers, this is all built-in empty zones. This will
enable them to return referrals to deeper in the tree.
</note>
<variablelist>
<varlistentry>
<term><command>empty-server</command></term>
<listitem>
<para>
Specify what server name will appear in the returned
SOA record for empty zones. If none is specified, then
the zone's name will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>empty-contact</command></term>
<listitem>
<para>
Specify what contact name will appear in the returned
SOA record for empty zones. If none is specified, then
"." will be used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>empty-zones-enable</command></term>
<listitem>
<para>
Enable or disable all empty zones. By default, they
are enabled.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>disable-empty-zone</command></term>
<listitem>
<para>
Disable individual empty zones. By default, none are
disabled. This option can be specified multiple times.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="acache">
<title>Additional Section Caching</title>
<para>
The additional section cache, also called <command>acache</command>,
is an internal cache to improve the response performance of BIND 9.
When additional section caching is enabled, BIND 9 will
cache an internal short-cut to the additional section content for
each answer RR.
Note that <command>acache</command> is an internal caching
mechanism of BIND 9, and is not related to the DNS caching
server function.
</para>
<para>
Additional section caching does not change the
response content (except the RRsets ordering of the additional
section, see below), but can improve the response performance
significantly.
It is particularly effective when BIND 9 acts as an authoritative
server for a zone that has many delegations with many glue RRs.
</para>
<para>
In order to obtain the maximum performance improvement
from additional section caching, setting
<command>additional-from-cache</command>
to <command>no</command> is recommended, since the current
implementation of <command>acache</command>
does not short-cut of additional section information from the
DNS cache data.
</para>
<para>
One obvious disadvantage of <command>acache</command> is
that it requires much more
memory for the internal cached data.
Thus, if the response performance does not matter and memory
consumption is much more critical, the
<command>acache</command> mechanism can be
disabled by setting <command>acache-enable</command> to
<command>no</command>.
It is also possible to specify the upper limit of memory
consumption
for acache by using <command>max-acache-size</command>.
</para>
<para>
Additional section caching also has a minor effect on the
RRset ordering in the additional section.
Without <command>acache</command>,
<command>cyclic</command> order is effective for the additional
section as well as the answer and authority sections.
However, additional section caching fixes the ordering when it
first caches an RRset for the additional section, and the same
ordering will be kept in succeeding responses, regardless of the
setting of <command>rrset-order</command>.
The effect of this should be minor, however, since an
RRset in the additional section
typically only contains a small number of RRs (and in many cases
it only contains a single RR), in which case the
ordering does not matter much.
</para>
<para>
The following is a summary of options related to
<command>acache</command>.
</para>
<variablelist>
<varlistentry>
<term><command>acache-enable</command></term>
<listitem>
<para>
If <command>yes</command>, additional section caching is
enabled. The default value is <command>no</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>acache-cleaning-interval</command></term>
<listitem>
<para>
The server will remove stale cache entries, based on an LRU
based
algorithm, every <command>acache-cleaning-interval</command> minutes.
The default is 60 minutes.
If set to 0, no periodic cleaning will occur.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-acache-size</command></term>
<listitem>
<para>
The maximum amount of memory in bytes to use for the server's acache.
When the amount of data in the acache reaches this limit,
the server
will clean more aggressively so that the limit is not
exceeded.
In a server with multiple views, the limit applies
separately to the
acache of each view.
The default is <literal>16M</literal>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3>
<title>Content Filtering</title>
<para>
<acronym>BIND</acronym> 9 provides the ability to filter
out DNS responses from external DNS servers containing
certain types of data in the answer section.
Specifically, it can reject address (A or AAAA) records if
the corresponding IPv4 or IPv6 addresses match the given
<varname>address_match_list</varname> of the
<command>deny-answer-addresses</command> option.
It can also reject CNAME or DNAME records if the "alias"
name (i.e., the CNAME alias or the substituted query name
due to DNAME) matches the
given <varname>namelist</varname> of the
<command>deny-answer-aliases</command> option, where
"match" means the alias name is a subdomain of one of
the <varname>name_list</varname> elements.
If the optional <varname>namelist</varname> is specified
with <command>except-from</command>, records whose query name
matches the list will be accepted regardless of the filter
setting.
Likewise, if the alias name is a subdomain of the
corresponding zone, the <command>deny-answer-aliases</command>
filter will not apply;
for example, even if "example.com" is specified for
<command>deny-answer-aliases</command>,
</para>
<programlisting>www.example.com. CNAME xxx.example.com.</programlisting>
<para>
returned by an "example.com" server will be accepted.
</para>
<para>
In the <varname>address_match_list</varname> of the
<command>deny-answer-addresses</command> option, only
<varname>ip_addr</varname>
and <varname>ip_prefix</varname>
are meaningful;
any <varname>key_id</varname> will be silently ignored.
</para>
<para>
If a response message is rejected due to the filtering,
the entire message is discarded without being cached, and
a SERVFAIL error will be returned to the client.
</para>
<para>
This filtering is intended to prevent "DNS rebinding attacks," in
which an attacker, in response to a query for a domain name the
attacker controls, returns an IP address within your own network or
an alias name within your own domain.
A naive web browser or script could then serve as an
unintended proxy, allowing the attacker
to get access to an internal node of your local network
that couldn't be externally accessed otherwise.
See the paper available at
<ulink>
http://portal.acm.org/citation.cfm?id=1315245.1315298
</ulink>
for more details about the attacks.
</para>
<para>
For example, if you own a domain named "example.net" and
your internal network uses an IPv4 prefix 192.0.2.0/24,
you might specify the following rules:
</para>
<programlisting>deny-answer-addresses { 192.0.2.0/24; } except-from { "example.net"; };
deny-answer-aliases { "example.net"; };
</programlisting>
<para>
If an external attacker lets a web browser in your local
network look up an IPv4 address of "attacker.example.com",
the attacker's DNS server would return a response like this:
</para>
<programlisting>attacker.example.com. A 192.0.2.1</programlisting>
<para>
in the answer section.
Since the rdata of this record (the IPv4 address) matches
the specified prefix 192.0.2.0/24, this response will be
ignored.
</para>
<para>
On the other hand, if the browser looks up a legitimate
internal web server "www.example.net" and the
following response is returned to
the <acronym>BIND</acronym> 9 server
</para>
<programlisting>www.example.net. A 192.0.2.2</programlisting>
<para>
it will be accepted since the owner name "www.example.net"
matches the <command>except-from</command> element,
"example.net".
</para>
<para>
Note that this is not really an attack on the DNS per se.
In fact, there is nothing wrong for an "external" name to
be mapped to your "internal" IP address or domain name
from the DNS point of view.
It might actually be provided for a legitimate purpose,
such as for debugging.
As long as the mapping is provided by the correct owner,
it is not possible or does not make sense to detect
whether the intent of the mapping is legitimate or not
within the DNS.
The "rebinding" attack must primarily be protected at the
application that uses the DNS.
For a large site, however, it may be difficult to protect
all possible applications at once.
This filtering feature is provided only to help such an
operational environment;
it is generally discouraged to turn it on unless you are
very sure you have no other choice and the attack is a
real threat for your applications.
</para>
<para>
Care should be particularly taken if you want to use this
option for addresses within 127.0.0.0/8.
These addresses are obviously "internal", but many
applications conventionally rely on a DNS mapping from
some name to such an address.
Filtering out DNS records containing this address
spuriously can break such applications.
</para>
</sect3>
<sect3>
<title>Response Policy Zone (RPZ) Rewriting</title>
<para>
<acronym>BIND</acronym> 9 includes an intentionally limited
mechanism to modify DNS responses for recursive requests
somewhat similar to email anti-spam DNS blacklists.
Responses can be changed to deny the existence of domains(NXDOMAIN),
deny the existence of IP addresses for domains (NODATA),
or contain other IP addresses or data.
</para>
<para>
The actions encoded in a response policy zone (RPZ) are applied
only to queries that ask for recursion (RD=1).
Response policy zones are named in the
<command>response-policy</command> option for the view or among the
global options if there is no response-policy option for the view.
RPZs are ordinary DNS zones containing RRsets
that can be queried normally if allowed.
It is usually best to restrict those queries with something like
<command>allow-query { localhost; };</command>.
</para>
<para>
There are four kinds of RPZ records, QNAME, IP, NSIP,
and NSDNAME.
QNAME records are applied to query names of requests and targets
of CNAME records resolved to generate the response.
The owner name of a QNAME RPZ record is the query name relativized
to the RPZ.
</para>
<para>
The second kind of RPZ record, an IP policy record,
is triggered by addresses in A and AAAA records
for the ANSWER sections of responses.
IP policy records have owner names that are
subdomains of <userinput>rpz-ip</userinput> relativized to the
RPZ origin name and encode an IP address or address block.
IPv4 addresses are encoded as
<userinput>prefixlength.B4.B3.B2.B1.rpz-ip</userinput>.
The prefix length must be between 1 and 32.
All four bytes, B4, B3, B2, and B1, must be present.
B4 is the decimal value of the least significant byte of the
IPv4 address as in IN-ADDR.ARPA.
IPv6 addresses are encoded in a format similar to the standard
IPv6 text representation,
<userinput>prefixlength.W8.W7.W6.W5.W4.W3.W2.W1.rpz-ip</userinput>.
Each of W8,...,W1 is a one to four digit hexadecimal number
representing 16 bits of the IPv6 address as in the standard text
representation of IPv6 addresses, but reversed as in IN-ADDR.ARPA.
All 8 words must be present except when consecutive
zero words are replaced with <userinput>.zz.</userinput>
analogous to double colons (::) in standard IPv6 text encodings.
The prefix length must be between 1 and 128.
</para>
<para>
NSDNAME policy records match names of authoritative servers
for the query name, a parent of the query name, a CNAME,
or a parent of a CNAME.
They are encoded as subdomains of
<userinput>rpz-nsdomain</userinput> relativized
to the RPZ origin name.
</para>
<para>
NSIP policy records match IP addresses in A and AAAA RRsets
for domains that can be checked against NSDNAME policy records.
The are encoded like IP policies except as subdomains of
<userinput>rpz-nsip</userinput>.
</para>
<para>
The query response is checked against all RPZs, so
two or more policy records can apply to a single response.
Because DNS responses can be rewritten according by at most a
single policy record, a single policy (other than
<command>DISABLED</command> policies) must be chosen.
Policies are chosen in the following order:
<itemizedlist>
<listitem>Among applicable zones, use the RPZ that appears first
in the response-policy option.
</listitem>
<listitem>Prefer QNAME to IP to NSDNAME to NSIP policy records
in a single RPZ
</listitem>
<listitem>Among applicable NSDNAME policy records, prefer the
policy record that matches the lexically smallest name
</listitem>
<listitem>Among IP or NSIP policy records, prefer the record
with the longest prefix.
</listitem>
<listitem>Among records with the same prefex length,
prefer the IP or NSIP policy record that matches
the smallest IP address.
</listitem>
</itemizedlist>
</para>
<para>
When the processing of a response is restarted to resolve
DNAME or CNAME records and an applicable policy record set has
not been found,
all RPZs are again consulted for the DNAME or CNAME names
and addresses.
</para>
<para>
Authority verification issues and variations in authority data
can cause inconsistent results for NSIP and NSDNAME policy records.
Glue NS records often differ from authoritative NS records.
So they are available
only when <acronym>BIND</acronym> is built with the
<userinput>--enable-rpz-nsip</userinput> or
<userinput>--enable-rpz-nsdname</userinput> options
on the "configure" command line.
</para>
<para>
RPZ record sets are special CNAME records or one or more
of any types of DNS record except DNAME or DNSSEC.
Except when a policy record is a CNAME, there can be more
more than one record and more than one type
in a set of policy records.
Except for three kinds of CNAME records that are illegal except
in policy zones, the records in a set are used in the response as if
their owner name were the query name. They are copied to the
response as dictated by their types.
<itemizedlist>
<listitem>A CNAME whose target is the root domain (.)
specifies the <command>NXDOMAIN</command> policy,
which generates an NXDOMAIN response.
</listitem>
<listitem>A CNAME whose target is the wildcard top-level
domain (*.) specifies the <command>NODATA</command> policy,
which rewrites the response to NODATA or ANCOUNT=1.
</listitem>
<listitem>A CNAME whose target is a wildcard hostname such
as *.example.com is used normally after the astrisk (*)
has been replaced with the query name.
These records are usually resolved with ordinary CNAMEs
outside the policy zones. They can be useful for logging.
</listitem>
<listitem>The <command>PASSTHRU</command> policy is specified
by a CNAME whose target is the variable part of its own
owner name. It causes the response to not be rewritten
and is most often used to "poke holes" in policies for
CIDR blocks.
</listitem>
</itemizedlist>
</para>
<para>
The policies specified in individual records
in an RPZ can be overridden with a <command>policy</command> clause
in the <command>response-policy</command> option.
An organization using an RPZ provided by another organization might
use this mechanism to redirect domains to its own walled garden.
<itemizedlist>
<listitem><command>GIVEN</command> says "do not override."
</listitem>
<listitem><command>DISABLED</command> causes policy records to do
nothing but log what they might have done.
The response to the DNS query will be written according to
any matching policy records that are not disabled.
Policy zones overridden with <command>DISABLED</command> should
appear first, because they will often not be logged
if a higher precedence policy is found first.
</listitem>
<listitem><command>PASSTHRU</command> causes all policy records
to act as if they were CNAME records with targets the variable
part of their owner name. They protect the response from
being changed.
</listitem>
<listitem><command>NXDOMAIN</command> causes all RPZ records
to specify NXDOMAIN policies.
</listitem>
<listitem><command>NODATA</command> overrides with the
NODATA policy
</listitem>
<listitem><command>CNAME domain</command> causes all RPZ
policy records to act as if they were "cname domain" records.
</listitem>
</itemizedlist>
</para>
<para>
For example, you might use this option statement
</para>
<programlisting> response-policy { zone "badlist"; };</programlisting>
<para>
and this zone statement
</para>
<programlisting> zone "badlist" {type master; file "master/badlist"; allow-query {none;}; };</programlisting>
<para>
with this zone file
</para>
<programlisting>$TTL 1H
@ SOA LOCALHOST. named-mgr.example.com (1 1h 15m 30d 2h)
NS LOCALHOST.
; QNAME policy records. There are no periods (.) after the owner names.
nxdomain.domain.com CNAME . ; NXDOMAIN policy
nodata.domain.com CNAME *. ; NODATA policy
bad.domain.com A 10.0.0.1 ; redirect to a walled garden
AAAA 2001:2::1
; do not rewrite (PASSTHRU) OK.DOMAIN.COM
ok.domain.com CNAME ok.domain.com.
bzone.domain.com CNAME garden.example.com.
; redirect x.bzone.domain.com to x.bzone.domain.com.garden.example.com
*.bzone.domain.com CNAME *.garden.example.com.
; IP policy records that rewrite all answers for 127/8 except 127.0.0.1
8.0.0.0.127.rpz-ip CNAME .
32.1.0.0.127.rpz-ip CNAME 32.1.0.0.127. ; PASSTHRU for 127.0.0.1
; NSDNAME and NSIP policy records
ns.domain.com.rpz-nsdname CNAME .
48.zz.2.2001.rpz-nsip CNAME .
</programlisting>
</sect3>
<sect3>
<title>Rate Limiting</title>
<para>
Excessive essentially identical UDP <emphasis>responses</emphasis>
can be discarded by configuring a
<command>rate-limit</command> clause in an
<command>options</command> statement.
This mechanism keeps BIND 9 from being used
in amplifying reflection denial of service attacks
as well as partially protecting BIND 9 itself from
some denial of service attacks.
Very short truncated responses can be sent to provide
rate-limited responses to legitimate
clients within a range of attacked and forged IP addresses,
Legitimate clients react to truncated response by retrying
with TCP.
</para>
<para>
Rate limiting works by setting
<command>responses-per-second</command>
to a number of repetitions per second for responses for a given name
and record type to a DNS client.
</para>
<para>
<command>Responses-per-second</command> is a limit on
identical responses instead of a limit on all responses or
even all responses to a single client.
10 identical responses per second is a generous limit except perhaps
when many clients are using a single IP address via network
address translation (NAT).
The default limit of zero specifies an unbounded limit to turn off
rate-limiting in a view or to only rate-limit NXDOMAIN or other
errors.
</para>
<para>
The notion of "identical responses"
and "single DNS client" cannot be simplistic.
All responses to a CIDR block with prefix
length specified with <command>IPv4-prefix-length</command>
(default 24) or <command>IPv6-prefix-length</command>
(default 56) are assumed to come from a single DNS client.
All empty (NODATA) responses for a valid domain,
regardless of query type, are identical.
Responses in the NODATA class are limited by
<command>nodata-per-second</command>
(default <command>responses-per-second</command>).
Requests for a name that result in DNS NXDOMAIN
errors are considered identical.
This controls some attacks using random names, but
accommodates servers that expect many legitimate NXDOMAIN responses
such as anti-spam blacklists.
By default the limit on NXDOMAIN errors is the same as the
<command>responses-per-second</command> value,
but it can be set separately with
<command>nxdomains-per-second</command>.
Referrals or delegations to the server of a given
domain are identical and are limited by
<command>referrals-per-second</command>
(default <command>responses-per-second</command>).
All requests for all names or types that result in DNS errors
such as SERVFAIL and FORMERR (but not NXDOMAIN) are considered
identical.
This controls attacks using invalid requests or distant,
broken authoritative servers.
By default the limit on errors is the same as the
<command>responses-per-second</command> value,
but it can be set separately with
<command>errors-per-second</command>.
</para>
<para>
Rate limiting uses a "credit" or "token bucket" scheme.
Each identical response has a conceptual account
that is given <command>responses-per-second</command>,
<command>errors-per-second</command>, and
<command>nxdomains-per-second</command> credits every second.
A DNS request triggering some desired response debits
the account by one.
Responses are not sent while the account is negative.
The account cannot become more positive than
the per-second limit
or more negative than <command>window</command>
times the per-second limit.
A DNS client that sends requests that are not
answered can be penalized for up to <command>window</command>
seconds (default 15).
</para>
<para>
Responses generated from local wildcards are counted and limited
as if they were for the parent domain name.
This prevents flooding by requesting random.wild.example.com.
For similar reasons, NXDOMAIN responses are counted and rate
limited by the valid domain name nearest to the
query name with an SOA record.
</para>
<para>
Many attacks using DNS involve UDP requests with forged source
addresses.
Rate limiting prevents the use of BIND 9 to flood a network
with responses to requests with forged source addresses,
but could let a third party block responses to legitimate requests.
There is a mechanism that can answer some legitimate
requests from a client whose address is being forged in a flood.
Setting <command>slip</command> to 2 (its default) causes every
other UDP request to be answered with a small response
claiming that the response would have been truncated.
The small size and relative infrequency of the response make
it unattractive for abuse.
<command>Slip</command> must be between 0 and 10.
A value of 0 does not "slip"
or sends no rate limiting truncated responses.
Some error responses includinge REFUSED and SERVFAIL
cannot be replaced with truncated responses and are instead
leaked at the <command>slip</command> rate.
</para>
<para>
When the approximate query per second rate exceeds
the <command>qps-scale</command> value,
then the <command>responses-per-second</command>,
<command>errors-per-second</command>,
<command>nxdomains-per-second</command> and
<command>all-per-second</command> values are reduced by the
ratio of the current rate to the <command>qps-scale</command> value.
This feature can tighten defenses during attacks.
For example, with
<command>qps-scale 250; responses-per-second 20;</command> and
a total query rate of 1000 queries/second for all queries from
all DNS clients including via TCP,
then the effective responses/second limit changes to
(250/1000)*20 or 5.
Responses sent via TCP are not limited
but are counted to compute the query per second rate.
</para>
<para>
Communities of DNS clients can be given their own parameters or no
rate limiting by putting
<command>rate-limit</command> statements in <command>view</command>
statements instead of the global <command>option</command>
statement.
A <command>rate-limit</command> statement in a view replaces
instead of being merged with a <command>rate-limit</command>
statement among the main options.
DNS clients within a view can be exempted from rate limits
with the <command>exempt-clients</command> clause.
</para>
<para>
UDP responses of all kinds can be limited with the
<command>all-per-second</command> phrase.
This rate limiting is unlike the rate limiting provided by
<command>responses-per-second</command>,
<command>errors-per-second</command>, and
<command>nxdomains-per-second</command> on a DNS server
which are often invisible to the victim of a DNS reflection attack.
Unless the forged requests of the attack are the same as the
legitimate requests of the victim, the victim's requests are
not affected.
Responses affected by an <command>all-per-second</command> limit
are always dropped; the <command>slip</command> value has no
effect.
An <command>all-per-second</command> limit should be
at least 4 times as large as the other limits,
because single DNS clients often send bursts of legitimate
requests.
For example, the receipt of a single mail message can prompt
requests from an SMTP server for NS, PTR, A, and AAAA records
as the incoming SMTP/TCP/IP connection is considered.
The SMTP server can need additional NS, A, AAAA, MX, TXT, and SPF
records as it considers the STMP <command>Mail From</command>
command.
Web browsers often repeatedly resolve the same names that
are repeated in HTML <IMG> tags in a page.
<command>All-per-second</command> is similar to the
rate limiting offered by firewalls but often inferior.
Attacks that justify ignoring the
contents of DNS responses are likely to be attacks on the
DNS server itself.
They usually should be discarded before the DNS server
spends resources make TCP connections or parsing DNS requesets,
but that rate limiting must be done before the
DNS server sees the requests.
</para>
<para>
The maximum size of the table used to track requests and
rate limit responses is set with <command>max-table-size</command>.
Each entry in the table is between 40 and 80 bytes.
The table needs approximately as many entries as the number
of requests received per second.
The default is 20,000.
To reduce the cold start of growing the table,
<command>min-table-size</command> (default 500)
can set the minimum table size.
Enable <command>rate-limit</command> category logging to monitor
expansions of the table and inform
choices for the initial and maximum table size.
</para>
<para>
Use <command>log-only yes</command> to test rate limiting parameters
without actually dropping any requests.
</para>
<para>
Responses dropped by rate limits are included in the
<command>RateDropped</command> and <command>QryDropped</command>
statistics.
Responses that truncated by rate limits are included in
<command>RateSlipped</command> and <command>RespTruncated</command>.
</para>
</sect3>
</sect2>
<sect2 id="server_statement_grammar">
<title><command>server</command> Statement Grammar</title>
<programlisting><command>server</command> <replaceable>ip_addr[/prefixlen]</replaceable> {
<optional> bogus <replaceable>yes_or_no</replaceable> ; </optional>
<optional> provide-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
<optional> request-ixfr <replaceable>yes_or_no</replaceable> ; </optional>
<optional> edns <replaceable>yes_or_no</replaceable> ; </optional>
<optional> edns-udp-size <replaceable>number</replaceable> ; </optional>
<optional> max-udp-size <replaceable>number</replaceable> ; </optional>
<optional> transfers <replaceable>number</replaceable> ; </optional>
<optional> transfer-format <replaceable>( one-answer | many-answers )</replaceable> ; ]</optional>
<optional> keys <replaceable>{ string ; <optional> string ; <optional>...</optional></optional> }</replaceable> ; </optional>
<optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> notify-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> notify-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> query-source <optional> address ( <replaceable>ip_addr</replaceable> | <replaceable>*</replaceable> ) </optional>
<optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional>; </optional>
<optional> query-source-v6 <optional> address ( <replaceable>ip_addr</replaceable> | <replaceable>*</replaceable> ) </optional>
<optional> port ( <replaceable>ip_port</replaceable> | <replaceable>*</replaceable> ) </optional>; </optional>
<optional> use-queryport-pool <replaceable>yes_or_no</replaceable>; </optional>
<optional> queryport-pool-ports <replaceable>number</replaceable>; </optional>
<optional> queryport-pool-updateinterval <replaceable>number</replaceable>; </optional>
};
</programlisting>
</sect2>
<sect2 id="server_statement_definition_and_usage">
<title><command>server</command> Statement Definition and
Usage</title>
<para>
The <command>server</command> statement defines
characteristics
to be associated with a remote name server. If a prefix length is
specified, then a range of servers is covered. Only the most
specific
server clause applies regardless of the order in
<filename>named.conf</filename>.
</para>
<para>
The <command>server</command> statement can occur at
the top level of the
configuration file or inside a <command>view</command>
statement.
If a <command>view</command> statement contains
one or more <command>server</command> statements, only
those
apply to the view and any top-level ones are ignored.
If a view contains no <command>server</command>
statements,
any top-level <command>server</command> statements are
used as
defaults.
</para>
<para>
If you discover that a remote server is giving out bad data,
marking it as bogus will prevent further queries to it. The
default
value of <command>bogus</command> is <command>no</command>.
</para>
<para>
The <command>provide-ixfr</command> clause determines
whether
the local server, acting as master, will respond with an
incremental
zone transfer when the given remote server, a slave, requests it.
If set to <command>yes</command>, incremental transfer
will be provided
whenever possible. If set to <command>no</command>,
all transfers
to the remote server will be non-incremental. If not set, the
value
of the <command>provide-ixfr</command> option in the
view or
global options block is used as a default.
</para>
<para>
The <command>request-ixfr</command> clause determines
whether
the local server, acting as a slave, will request incremental zone
transfers from the given remote server, a master. If not set, the
value of the <command>request-ixfr</command> option in
the view or
global options block is used as a default.
</para>
<para>
IXFR requests to servers that do not support IXFR will
automatically
fall back to AXFR. Therefore, there is no need to manually list
which servers support IXFR and which ones do not; the global
default
of <command>yes</command> should always work.
The purpose of the <command>provide-ixfr</command> and
<command>request-ixfr</command> clauses is
to make it possible to disable the use of IXFR even when both
master
and slave claim to support it, for example if one of the servers
is buggy and crashes or corrupts data when IXFR is used.
</para>
<para>
The <command>edns</command> clause determines whether
the local server will attempt to use EDNS when communicating
with the remote server. The default is <command>yes</command>.
</para>
<para>
The <command>edns-udp-size</command> option sets the EDNS UDP size
that is advertised by <command>named</command> when querying the remote server.
Valid values are 512 to 4096 bytes (values outside this range will be
silently adjusted). This option is useful when you wish to
advertises a different value to this server than the value you
advertise globally, for example, when there is a firewall at the
remote site that is blocking large replies.
</para>
<para>
The <command>max-udp-size</command> option sets the
maximum EDNS UDP message size <command>named</command> will send. Valid
values are 512 to 4096 bytes (values outside this range will
be silently adjusted). This option is useful when you
know that there is a firewall that is blocking large
replies from <command>named</command>.
</para>
<para>
The server supports two zone transfer methods. The first, <command>one-answer</command>,
uses one DNS message per resource record transferred. <command>many-answers</command> packs
as many resource records as possible into a message. <command>many-answers</command> is
more efficient, but is only known to be understood by <acronym>BIND</acronym> 9, <acronym>BIND</acronym>
8.x, and patched versions of <acronym>BIND</acronym>
4.9.5. You can specify which method
to use for a server with the <command>transfer-format</command> option.
If <command>transfer-format</command> is not
specified, the <command>transfer-format</command>
specified
by the <command>options</command> statement will be
used.
</para>
<para><command>transfers</command>
is used to limit the number of concurrent inbound zone
transfers from the specified server. If no
<command>transfers</command> clause is specified, the
limit is set according to the
<command>transfers-per-ns</command> option.
</para>
<para>
The <command>keys</command> clause identifies a
<command>key_id</command> defined by the <command>key</command> statement,
to be used for transaction security (TSIG, <xref linkend="tsig"/>)
when talking to the remote server.
When a request is sent to the remote server, a request signature
will be generated using the key specified here and appended to the
message. A request originating from the remote server is not
required
to be signed by this key.
</para>
<para>
Although the grammar of the <command>keys</command>
clause
allows for multiple keys, only a single key per server is
currently
supported.
</para>
<para>
The <command>transfer-source</command> and
<command>transfer-source-v6</command> clauses specify
the IPv4 and IPv6 source
address to be used for zone transfer with the remote server,
respectively.
For an IPv4 remote server, only <command>transfer-source</command> can
be specified.
Similarly, for an IPv6 remote server, only
<command>transfer-source-v6</command> can be
specified.
For more details, see the description of
<command>transfer-source</command> and
<command>transfer-source-v6</command> in
<xref linkend="zone_transfers"/>.
</para>
<para>
The <command>notify-source</command> and
<command>notify-source-v6</command> clauses specify the
IPv4 and IPv6 source address to be used for notify
messages sent to remote servers, respectively. For an
IPv4 remote server, only <command>notify-source</command>
can be specified. Similarly, for an IPv6 remote server,
only <command>notify-source-v6</command> can be specified.
</para>
<para>
The <command>query-source</command> and
<command>query-source-v6</command> clauses specify the
IPv4 and IPv6 source address to be used for queries
sent to remote servers, respectively. For an IPv4
remote server, only <command>query-source</command> can
be specified. Similarly, for an IPv6 remote server,
only <command>query-source-v6</command> can be specified.
</para>
</sect2>
<sect2 id="statschannels">
<title><command>statistics-channels</command> Statement Grammar</title>
<programlisting><command>statistics-channels</command> {
[ inet ( ip_addr | * ) [ port ip_port ]
[ allow { <replaceable> address_match_list </replaceable> } ]; ]
[ inet ...; ]
};
</programlisting>
</sect2>
<sect2>
<title><command>statistics-channels</command> Statement Definition and
Usage</title>
<para>
The <command>statistics-channels</command> statement
declares communication channels to be used by system
administrators to get access to statistics information of
the name server.
</para>
<para>
This statement intends to be flexible to support multiple
communication protocols in the future, but currently only
HTTP access is supported.
It requires that BIND 9 be compiled with libxml2;
the <command>statistics-channels</command> statement is
still accepted even if it is built without the library,
but any HTTP access will fail with an error.
</para>
<para>
An <command>inet</command> control channel is a TCP socket
listening at the specified <command>ip_port</command> on the
specified <command>ip_addr</command>, which can be an IPv4 or IPv6
address. An <command>ip_addr</command> of <literal>*</literal> (asterisk) is
interpreted as the IPv4 wildcard address; connections will be
accepted on any of the system's IPv4 addresses.
To listen on the IPv6 wildcard address,
use an <command>ip_addr</command> of <literal>::</literal>.
</para>
<para>
If no port is specified, port 80 is used for HTTP channels.
The asterisk "<literal>*</literal>" cannot be used for
<command>ip_port</command>.
</para>
<para>
The attempt of opening a statistics channel is
restricted by the optional <command>allow</command> clause.
Connections to the statistics channel are permitted based on the
<command>address_match_list</command>.
If no <command>allow</command> clause is present,
<command>named</command> accepts connection
attempts from any address; since the statistics may
contain sensitive internal information, it is highly
recommended to restrict the source of connection requests
appropriately.
</para>
<para>
If no <command>statistics-channels</command> statement is present,
<command>named</command> will not open any communication channels.
</para>
</sect2>
<sect2 id="trusted-keys">
<title><command>trusted-keys</command> Statement Grammar</title>
<programlisting><command>trusted-keys</command> {
<replaceable>string</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ;
<optional> <replaceable>string</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; <optional>...</optional></optional>
};
</programlisting>
</sect2>
<sect2>
<title><command>trusted-keys</command> Statement Definition
and Usage</title>
<para>
The <command>trusted-keys</command> statement defines
DNSSEC security roots. DNSSEC is described in <xref
linkend="DNSSEC"/>. A security root is defined when the
public key for a non-authoritative zone is known, but
cannot be securely obtained through DNS, either because
it is the DNS root zone or because its parent zone is
unsigned. Once a key has been configured as a trusted
key, it is treated as if it had been validated and
proven secure. The resolver attempts DNSSEC validation
on all DNS data in subdomains of a security root.
</para>
<para>
All keys (and corresponding zones) listed in
<command>trusted-keys</command> are deemed to exist regardless
of what parent zones say. Similarly for all keys listed in
<command>trusted-keys</command> only those keys are
used to validate the DNSKEY RRset. The parent's DS RRset
will not be used.
</para>
<para>
The <command>trusted-keys</command> statement can contain
multiple key entries, each consisting of the key's
domain name, flags, protocol, algorithm, and the Base-64
representation of the key data.
Spaces, tabs, newlines and carriage returns are ignored
in the key data, so the configuration may be split up into
multiple lines.
</para>
<para>
<command>trusted-keys</command> may be set at the top level
of <filename>named.conf</filename> or within a view. If it is
set in both places, they are additive: keys defined at the top
level are inherited by all views, but keys defined in a view
are only used within that view.
</para>
</sect2>
<sect2>
<title><command>managed-keys</command> Statement Grammar</title>
<programlisting><command>managed-keys</command> {
<replaceable>string</replaceable> initial-key <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ;
<optional> <replaceable>string</replaceable> initial-key <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; <optional>...</optional></optional>
};
</programlisting>
</sect2>
<sect2 id="managed-keys">
<title><command>managed-keys</command> Statement Definition
and Usage</title>
<para>
The <command>managed-keys</command> statement, like
<command>trusted-keys</command>, defines DNSSEC
security roots. The difference is that
<command>managed-keys</command> can be kept up to date
automatically, without intervention from the resolver
operator.
</para>
<para>
Suppose, for example, that a zone's key-signing
key was compromised, and the zone owner had to revoke and
replace the key. A resolver which had the old key in a
<command>trusted-keys</command> statement would be
unable to validate this zone any longer; it would
reply with a SERVFAIL response code. This would
continue until the resolver operator had updated the
<command>trusted-keys</command> statement with the new key.
</para>
<para>
If, however, the zone were listed in a
<command>managed-keys</command> statement instead, then the
zone owner could add a "stand-by" key to the zone in advance.
<command>named</command> would store the stand-by key, and
when the original key was revoked, <command>named</command>
would be able to transition smoothly to the new key. It would
also recognize that the old key had been revoked, and cease
using that key to validate answers, minimizing the damage that
the compromised key could do.
</para>
<para>
A <command>managed-keys</command> statement contains a list of
the keys to be managed, along with information about how the
keys are to be initialized for the first time. The only
initialization method currently supported (as of
<acronym>BIND</acronym> 9.7.0) is <literal>initial-key</literal>.
This means the <command>managed-keys</command> statement must
contain a copy of the initializing key. (Future releases may
allow keys to be initialized by other methods, eliminating this
requirement.)
</para>
<para>
Consequently, a <command>managed-keys</command> statement
appears similar to a <command>trusted-keys</command>, differing
in the presence of the second field, containing the keyword
<literal>initial-key</literal>. The difference is, whereas the
keys listed in a <command>trusted-keys</command> continue to be
trusted until they are removed from
<filename>named.conf</filename>, an initializing key listed
in a <command>managed-keys</command> statement is only trusted
<emphasis>once</emphasis>: for as long as it takes to load the
managed key database and start the RFC 5011 key maintenance
process.
</para>
<para>
The first time <command>named</command> runs with a managed key
configured in <filename>named.conf</filename>, it fetches the
DNSKEY RRset directly from the zone apex, and validates it
using the key specified in the <command>managed-keys</command>
statement. If the DNSKEY RRset is validly signed, then it is
used as the basis for a new managed keys database.
</para>
<para>
From that point on, whenever <command>named</command> runs, it
sees the <command>managed-keys</command> statement, checks to
make sure RFC 5011 key maintenance has already been initialized
for the specified domain, and if so, it simply moves on. The
key specified in the <command>managed-keys</command> is not
used to validate answers; it has been superseded by the key or
keys stored in the managed keys database.
</para>
<para>
The next time <command>named</command> runs after a name
has been <emphasis>removed</emphasis> from the
<command>managed-keys</command> statement, the corresponding
zone will be removed from the managed keys database,
and RFC 5011 key maintenance will no longer be used for that
domain.
</para>
<para>
<command>named</command> only maintains a single managed keys
database; consequently, unlike <command>trusted-keys</command>,
<command>managed-keys</command> may only be set at the top
level of <filename>named.conf</filename>, not within a view.
</para>
<para>
In the current implementation, the managed keys database is
stored as a master-format zone file called
<filename>managed-keys.bind</filename>. When the key database
is changed, the zone is updated. As with any other dynamic
zone, changes will be written into a journal file,
<filename>managed-keys.bind.jnl</filename>. They are committed
to the master file as soon as possible afterward; in the case
of the managed key database, this will usually occur within 30
seconds. So, whenever <command>named</command> is using
automatic key maintenance, those two files can be expected to
exist in the working directory. (For this reason among others,
the working directory should be always be writable by
<command>named</command>.)
</para>
<para>
If the <command>dnssec-lookaside</command> option is
set to <userinput>auto</userinput>, <command>named</command>
will automatically initialize a managed key for the
zone <literal>dlv.isc.org</literal>. The key that is
used to initialize the key maintenance process is built
into <command>named</command>, and can be overridden
from <command>bindkeys-file</command>.
</para>
</sect2>
<sect2 id="view_statement_grammar">
<title><command>view</command> Statement Grammar</title>
<programlisting><command>view</command> <replaceable>view_name</replaceable>
<optional><replaceable>class</replaceable></optional> {
match-clients { <replaceable>address_match_list</replaceable> };
match-destinations { <replaceable>address_match_list</replaceable> };
match-recursive-only <replaceable>yes_or_no</replaceable> ;
<optional> <replaceable>view_option</replaceable>; ...</optional>
<optional> <replaceable>zone_statement</replaceable>; ...</optional>
};
</programlisting>
</sect2>
<sect2>
<title><command>view</command> Statement Definition and Usage</title>
<para>
The <command>view</command> statement is a powerful
feature
of <acronym>BIND</acronym> 9 that lets a name server
answer a DNS query differently
depending on who is asking. It is particularly useful for
implementing
split DNS setups without having to run multiple servers.
</para>
<para>
Each <command>view</command> statement defines a view
of the
DNS namespace that will be seen by a subset of clients. A client
matches
a view if its source IP address matches the
<varname>address_match_list</varname> of the view's
<command>match-clients</command> clause and its
destination IP address matches
the <varname>address_match_list</varname> of the
view's
<command>match-destinations</command> clause. If not
specified, both
<command>match-clients</command> and <command>match-destinations</command>
default to matching all addresses. In addition to checking IP
addresses
<command>match-clients</command> and <command>match-destinations</command>
can also take <command>keys</command> which provide an
mechanism for the
client to select the view. A view can also be specified
as <command>match-recursive-only</command>, which
means that only recursive
requests from matching clients will match that view.
The order of the <command>view</command> statements is
significant —
a client request will be resolved in the context of the first
<command>view</command> that it matches.
</para>
<para>
Zones defined within a <command>view</command>
statement will
only be accessible to clients that match the <command>view</command>.
By defining a zone of the same name in multiple views, different
zone data can be given to different clients, for example,
"internal"
and "external" clients in a split DNS setup.
</para>
<para>
Many of the options given in the <command>options</command> statement
can also be used within a <command>view</command>
statement, and then
apply only when resolving queries with that view. When no
view-specific
value is given, the value in the <command>options</command> statement
is used as a default. Also, zone options can have default values
specified
in the <command>view</command> statement; these
view-specific defaults
take precedence over those in the <command>options</command> statement.
</para>
<para>
Views are class specific. If no class is given, class IN
is assumed. Note that all non-IN views must contain a hint zone,
since only the IN class has compiled-in default hints.
</para>
<para>
If there are no <command>view</command> statements in
the config
file, a default view that matches any client is automatically
created
in class IN. Any <command>zone</command> statements
specified on
the top level of the configuration file are considered to be part
of
this default view, and the <command>options</command>
statement will
apply to the default view. If any explicit <command>view</command>
statements are present, all <command>zone</command>
statements must
occur inside <command>view</command> statements.
</para>
<para>
Here is an example of a typical split DNS setup implemented
using <command>view</command> statements:
</para>
<programlisting>view "internal" {
// This should match our internal networks.
match-clients { 10.0.0.0/8; };
// Provide recursive service to internal
// clients only.
recursion yes;
// Provide a complete view of the example.com
// zone including addresses of internal hosts.
zone "example.com" {
type master;
file "example-internal.db";
};
};
view "external" {
// Match all clients not matched by the
// previous view.
match-clients { any; };
// Refuse recursive service to external clients.
recursion no;
// Provide a restricted view of the example.com
// zone containing only publicly accessible hosts.
zone "example.com" {
type master;
file "example-external.db";
};
};
</programlisting>
</sect2>
<sect2 id="zone_statement_grammar">
<title><command>zone</command>
Statement Grammar</title>
<programlisting><command>zone</command> <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type master;
<optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query-on { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-transfer { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-update { <replaceable>address_match_list</replaceable> }; </optional>
<optional> update-policy <replaceable>local</replaceable> | { <replaceable>update_policy_rule</replaceable> <optional>...</optional> }; </optional>
<optional> also-notify { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ;
<optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> check-names (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional>
<optional> check-mx (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional>
<optional> check-wildcard <replaceable>yes_or_no</replaceable>; </optional>
<optional> check-integrity <replaceable>yes_or_no</replaceable> ; </optional>
<optional> dialup <replaceable>dialup_option</replaceable> ; </optional>
<optional> file <replaceable>string</replaceable> ; </optional>
<optional> masterfile-format (<constant>text</constant>|<constant>raw</constant>) ; </optional>
<optional> journal <replaceable>string</replaceable> ; </optional>
<optional> max-journal-size <replaceable>size_spec</replaceable>; </optional>
<optional> forward (<constant>only</constant>|<constant>first</constant>) ; </optional>
<optional> forwarders { <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> ixfr-base <replaceable>string</replaceable> ; </optional>
<optional> ixfr-from-differences <replaceable>yes_or_no</replaceable>; </optional>
<optional> ixfr-tmp-file <replaceable>string</replaceable> ; </optional>
<optional> maintain-ixfr-base <replaceable>yes_or_no</replaceable> ; </optional>
<optional> max-ixfr-log-size <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-idle-out <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-time-out <replaceable>number</replaceable> ; </optional>
<optional> notify <replaceable>yes_or_no</replaceable> | <replaceable>explicit</replaceable> | <replaceable>master-only</replaceable> ; </optional>
<optional> notify-delay <replaceable>seconds</replaceable> ; </optional>
<optional> notify-to-soa <replaceable>yes_or_no</replaceable>; </optional>
<optional> pubkey <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; </optional>
<optional> notify-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> notify-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> zone-statistics <replaceable>yes_or_no</replaceable> ; </optional>
<optional> sig-validity-interval <replaceable>number</replaceable> <optional><replaceable>number</replaceable></optional> ; </optional>
<optional> sig-signing-nodes <replaceable>number</replaceable> ; </optional>
<optional> sig-signing-signatures <replaceable>number</replaceable> ; </optional>
<optional> sig-signing-type <replaceable>number</replaceable> ; </optional>
<optional> database <replaceable>string</replaceable> ; </optional>
<optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> min-retry-time <replaceable>number</replaceable> ; </optional>
<optional> max-retry-time <replaceable>number</replaceable> ; </optional>
<optional> key-directory <replaceable>path_name</replaceable>; </optional>
<optional> auto-dnssec <constant>allow</constant>|<constant>maintain</constant>|<constant>off</constant>; </optional>
<optional> zero-no-soa-ttl <replaceable>yes_or_no</replaceable> ; </optional>
};
zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type slave;
<optional> allow-notify { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query-on { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-transfer { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-update-forwarding { <replaceable>address_match_list</replaceable> }; </optional>
<optional> update-check-ksk <replaceable>yes_or_no</replaceable>; </optional>
<optional> dnssec-update-mode ( <replaceable>maintain</replaceable> | <replaceable>no-resign</replaceable> ); </optional>
<optional> dnssec-dnskey-kskonly <replaceable>yes_or_no</replaceable>; </optional>
<optional> dnssec-secure-to-insecure <replaceable>yes_or_no</replaceable> ; </optional>
<optional> try-tcp-refresh <replaceable>yes_or_no</replaceable>; </optional>
<optional> also-notify { <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ;
<optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> check-names (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional>
<optional> dialup <replaceable>dialup_option</replaceable> ; </optional>
<optional> file <replaceable>string</replaceable> ; </optional>
<optional> masterfile-format (<constant>text</constant>|<constant>raw</constant>) ; </optional>
<optional> journal <replaceable>string</replaceable> ; </optional>
<optional> max-journal-size <replaceable>size_spec</replaceable>; </optional>
<optional> forward (<constant>only</constant>|<constant>first</constant>) ; </optional>
<optional> forwarders { <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> ixfr-base <replaceable>string</replaceable> ; </optional>
<optional> ixfr-from-differences <replaceable>yes_or_no</replaceable>; </optional>
<optional> ixfr-tmp-file <replaceable>string</replaceable> ; </optional>
<optional> maintain-ixfr-base <replaceable>yes_or_no</replaceable> ; </optional>
<optional> masters <optional>port <replaceable>ip_port</replaceable></optional> { ( <replaceable>masters_list</replaceable> | <replaceable>ip_addr</replaceable>
<optional>port <replaceable>ip_port</replaceable></optional>
<optional>key <replaceable>key</replaceable></optional> ) ; <optional>...</optional> }; </optional>
<optional> max-ixfr-log-size <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-idle-in <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-idle-out <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-time-in <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-time-out <replaceable>number</replaceable> ; </optional>
<optional> notify <replaceable>yes_or_no</replaceable> | <replaceable>explicit</replaceable> | <replaceable>master-only</replaceable> ; </optional>
<optional> notify-delay <replaceable>seconds</replaceable> ; </optional>
<optional> notify-to-soa <replaceable>yes_or_no</replaceable>; </optional>
<optional> pubkey <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; </optional>
<optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> alt-transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> alt-transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>)
<optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> use-alt-transfer-source <replaceable>yes_or_no</replaceable>; </optional>
<optional> notify-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> notify-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> zone-statistics <replaceable>yes_or_no</replaceable> ; </optional>
<optional> database <replaceable>string</replaceable> ; </optional>
<optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> min-retry-time <replaceable>number</replaceable> ; </optional>
<optional> max-retry-time <replaceable>number</replaceable> ; </optional>
<optional> multi-master <replaceable>yes_or_no</replaceable> ; </optional>
<optional> zero-no-soa-ttl <replaceable>yes_or_no</replaceable> ; </optional>
};
zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type hint;
file <replaceable>string</replaceable> ;
<optional> delegation-only <replaceable>yes_or_no</replaceable> ; </optional>
<optional> check-names (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional> // Not Implemented.
};
zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type stub;
<optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
<optional> allow-query-on { <replaceable>address_match_list</replaceable> }; </optional>
<optional> check-names (<constant>warn</constant>|<constant>fail</constant>|<constant>ignore</constant>) ; </optional>
<optional> dialup <replaceable>dialup_option</replaceable> ; </optional>
<optional> delegation-only <replaceable>yes_or_no</replaceable> ; </optional>
<optional> file <replaceable>string</replaceable> ; </optional>
<optional> masterfile-format (<constant>text</constant>|<constant>raw</constant>) ; </optional>
<optional> forward (<constant>only</constant>|<constant>first</constant>) ; </optional>
<optional> forwarders { <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> masters <optional>port <replaceable>ip_port</replaceable></optional> { ( <replaceable>masters_list</replaceable> | <replaceable>ip_addr</replaceable>
<optional>port <replaceable>ip_port</replaceable></optional>
<optional>key <replaceable>key</replaceable></optional> ) ; <optional>...</optional> }; </optional>
<optional> max-transfer-idle-in <replaceable>number</replaceable> ; </optional>
<optional> max-transfer-time-in <replaceable>number</replaceable> ; </optional>
<optional> pubkey <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>number</replaceable> <replaceable>string</replaceable> ; </optional>
<optional> transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>)
<optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> alt-transfer-source (<replaceable>ip4_addr</replaceable> | <constant>*</constant>) <optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> alt-transfer-source-v6 (<replaceable>ip6_addr</replaceable> | <constant>*</constant>)
<optional>port <replaceable>ip_port</replaceable></optional> ; </optional>
<optional> use-alt-transfer-source <replaceable>yes_or_no</replaceable>; </optional>
<optional> zone-statistics <replaceable>yes_or_no</replaceable> ; </optional>
<optional> database <replaceable>string</replaceable> ; </optional>
<optional> min-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> max-refresh-time <replaceable>number</replaceable> ; </optional>
<optional> min-retry-time <replaceable>number</replaceable> ; </optional>
<optional> max-retry-time <replaceable>number</replaceable> ; </optional>
<optional> multi-master <replaceable>yes_or_no</replaceable> ; </optional>
};
zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type static-stub;
<optional> allow-query { <replaceable>address_match_list</replaceable> }; </optional>
<optional> server-addresses { <optional> <replaceable>ip_addr</replaceable> ; ... </optional> }; </optional>
<optional> server-names { <optional> <replaceable>namelist</replaceable> </optional> }; </optional>
<optional> zone-statistics <replaceable>yes_or_no</replaceable> ; </optional>
};
zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type forward;
<optional> forward (<constant>only</constant>|<constant>first</constant>) ; </optional>
<optional> forwarders { <optional> <replaceable>ip_addr</replaceable> <optional>port <replaceable>ip_port</replaceable></optional> ; ... </optional> }; </optional>
<optional> delegation-only <replaceable>yes_or_no</replaceable> ; </optional>
};
zone <replaceable>zone_name</replaceable> <optional><replaceable>class</replaceable></optional> {
type delegation-only;
};
</programlisting>
</sect2>
<sect2>
<title><command>zone</command> Statement Definition and Usage</title>
<sect3>
<title>Zone Types</title>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<!--colspec colname="1" colnum="1" colsep="0" colwidth="1.108in"/-->
<!--colspec colname="2" colnum="2" colsep="0" colwidth="4.017in"/-->
<colspec colname="1" colnum="1" colsep="0"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.017in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<varname>master</varname>
</para>
</entry>
<entry colname="2">
<para>
The server has a master copy of the data
for the zone and will be able to provide authoritative
answers for
it.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>slave</varname>
</para>
</entry>
<entry colname="2">
<para>
A slave zone is a replica of a master
zone. The <command>masters</command> list
specifies one or more IP addresses
of master servers that the slave contacts to update
its copy of the zone.
Masters list elements can also be names of other
masters lists.
By default, transfers are made from port 53 on the
servers; this can
be changed for all servers by specifying a port number
before the
list of IP addresses, or on a per-server basis after
the IP address.
Authentication to the master can also be done with
per-server TSIG keys.
If a file is specified, then the
replica will be written to this file whenever the zone
is changed,
and reloaded from this file on a server restart. Use
of a file is
recommended, since it often speeds server startup and
eliminates
a needless waste of bandwidth. Note that for large
numbers (in the
tens or hundreds of thousands) of zones per server, it
is best to
use a two-level naming scheme for zone filenames. For
example,
a slave server for the zone <literal>example.com</literal> might place
the zone contents into a file called
<filename>ex/example.com</filename> where <filename>ex/</filename> is
just the first two letters of the zone name. (Most
operating systems
behave very slowly if you put 100000 files into
a single directory.)
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>stub</varname>
</para>
</entry>
<entry colname="2">
<para>
A stub zone is similar to a slave zone,
except that it replicates only the NS records of a
master zone instead
of the entire zone. Stub zones are not a standard part
of the DNS;
they are a feature specific to the <acronym>BIND</acronym> implementation.
</para>
<para>
Stub zones can be used to eliminate the need for glue
NS record
in a parent zone at the expense of maintaining a stub
zone entry and
a set of name server addresses in <filename>named.conf</filename>.
This usage is not recommended for new configurations,
and BIND 9
supports it only in a limited way.
In <acronym>BIND</acronym> 4/8, zone
transfers of a parent zone
included the NS records from stub children of that
zone. This meant
that, in some cases, users could get away with
configuring child stubs
only in the master server for the parent zone. <acronym>BIND</acronym>
9 never mixes together zone data from different zones
in this
way. Therefore, if a <acronym>BIND</acronym> 9 master serving a parent
zone has child stub zones configured, all the slave
servers for the
parent zone also need to have the same child stub
zones
configured.
</para>
<para>
Stub zones can also be used as a way of forcing the
resolution
of a given domain to use a particular set of
authoritative servers.
For example, the caching name servers on a private
network using
RFC1918 addressing may be configured with stub zones
for
<literal>10.in-addr.arpa</literal>
to use a set of internal name servers as the
authoritative
servers for that domain.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>static-stub</varname>
</para>
</entry>
<entry colname="2">
<para>
A static-stub zone is similar to a stub zone
with the following exceptions:
the zone data is statically configured, rather
than transferred from a master server;
when recursion is necessary for a query that
matches a static-stub zone, the locally
configured data (nameserver names and glue addresses)
is always used even if different authoritative
information is cached.
</para>
<para>
Zone data is configured via the
<command>server-addresses</command> and
<command>server-names</command> zone options.
</para>
<para>
The zone data is maintained in the form of NS
and (if necessary) glue A or AAAA RRs
internally, which can be seen by dumping zone
databases by <command>rndc dumpdb -all</command>.
The configured RRs are considered local configuration
parameters rather than public data.
Non recursive queries (i.e., those with the RD
bit off) to a static-stub zone are therefore
prohibited and will be responded with REFUSED.
</para>
<para>
Since the data is statically configured, no
zone maintenance action takes place for a static-stub
zone.
For example, there is no periodic refresh
attempt, and an incoming notify message
will be rejected with an rcode of NOTAUTH.
</para>
<para>
Each static-stub zone is configured with
internally generated NS and (if necessary)
glue A or AAAA RRs
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>forward</varname>
</para>
</entry>
<entry colname="2">
<para>
A "forward zone" is a way to configure
forwarding on a per-domain basis. A <command>zone</command> statement
of type <command>forward</command> can
contain a <command>forward</command>
and/or <command>forwarders</command>
statement,
which will apply to queries within the domain given by
the zone
name. If no <command>forwarders</command>
statement is present or
an empty list for <command>forwarders</command> is given, then no
forwarding will be done for the domain, canceling the
effects of
any forwarders in the <command>options</command> statement. Thus
if you want to use this type of zone to change the
behavior of the
global <command>forward</command> option
(that is, "forward first"
to, then "forward only", or vice versa, but want to
use the same
servers as set globally) you need to re-specify the
global forwarders.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>hint</varname>
</para>
</entry>
<entry colname="2">
<para>
The initial set of root name servers is
specified using a "hint zone". When the server starts
up, it uses
the root hints to find a root name server and get the
most recent
list of root name servers. If no hint zone is
specified for class
IN, the server uses a compiled-in default set of root
servers hints.
Classes other than IN have no built-in defaults hints.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>delegation-only</varname>
</para>
</entry>
<entry colname="2">
<para>
This is used to enforce the delegation-only
status of infrastructure zones (e.g. COM,
NET, ORG). Any answer that is received
without an explicit or implicit delegation
in the authority section will be treated
as NXDOMAIN. This does not apply to the
zone apex. This should not be applied to
leaf zones.
</para>
<para>
<varname>delegation-only</varname> has no
effect on answers received from forwarders.
</para>
<para>
See caveats in <xref linkend="root_delegation_only"/>.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>Class</title>
<para>
The zone's name may optionally be followed by a class. If
a class is not specified, class <literal>IN</literal> (for <varname>Internet</varname>),
is assumed. This is correct for the vast majority of cases.
</para>
<para>
The <literal>hesiod</literal> class is
named for an information service from MIT's Project Athena. It
is
used to share information about various systems databases, such
as users, groups, printers and so on. The keyword
<literal>HS</literal> is
a synonym for hesiod.
</para>
<para>
Another MIT development is Chaosnet, a LAN protocol created
in the mid-1970s. Zone data for it can be specified with the <literal>CHAOS</literal> class.
</para>
</sect3>
<sect3>
<title>Zone Options</title>
<variablelist>
<varlistentry>
<term><command>allow-notify</command></term>
<listitem>
<para>
See the description of
<command>allow-notify</command> in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query</command></term>
<listitem>
<para>
See the description of
<command>allow-query</command> in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-query-on</command></term>
<listitem>
<para>
See the description of
<command>allow-query-on</command> in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-transfer</command></term>
<listitem>
<para>
See the description of <command>allow-transfer</command>
in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update</command></term>
<listitem>
<para>
See the description of <command>allow-update</command>
in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>update-policy</command></term>
<listitem>
<para>
Specifies a "Simple Secure Update" policy. See
<xref linkend="dynamic_update_policies"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>allow-update-forwarding</command></term>
<listitem>
<para>
See the description of <command>allow-update-forwarding</command>
in <xref linkend="access_control"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>also-notify</command></term>
<listitem>
<para>
Only meaningful if <command>notify</command>
is
active for this zone. The set of machines that will
receive a
<literal>DNS NOTIFY</literal> message
for this zone is made up of all the listed name servers
(other than
the primary master) for the zone plus any IP addresses
specified
with <command>also-notify</command>. A port
may be specified
with each <command>also-notify</command>
address to send the notify
messages to a port other than the default of 53.
<command>also-notify</command> is not
meaningful for stub zones.
The default is the empty list.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-names</command></term>
<listitem>
<para>
This option is used to restrict the character set and
syntax of
certain domain names in master files and/or DNS responses
received from the
network. The default varies according to zone type. For <command>master</command> zones the default is <command>fail</command>. For <command>slave</command>
zones the default is <command>warn</command>.
It is not implemented for <command>hint</command> zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-mx</command></term>
<listitem>
<para>
See the description of
<command>check-mx</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-wildcard</command></term>
<listitem>
<para>
See the description of
<command>check-wildcard</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-integrity</command></term>
<listitem>
<para>
See the description of
<command>check-integrity</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>check-sibling</command></term>
<listitem>
<para>
See the description of
<command>check-sibling</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zero-no-soa-ttl</command></term>
<listitem>
<para>
See the description of
<command>zero-no-soa-ttl</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>update-check-ksk</command></term>
<listitem>
<para>
See the description of
<command>update-check-ksk</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-dnskey-kskonly</command></term>
<listitem>
<para>
See the description of
<command>dnssec-dnskey-kskonly</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>try-tcp-refresh</command></term>
<listitem>
<para>
See the description of
<command>try-tcp-refresh</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>database</command></term>
<listitem>
<para>
Specify the type of database to be used for storing the
zone data. The string following the <command>database</command> keyword
is interpreted as a list of whitespace-delimited words.
The first word
identifies the database type, and any subsequent words are
passed
as arguments to the database to be interpreted in a way
specific
to the database type.
</para>
<para>
The default is <userinput>"rbt"</userinput>, BIND 9's
native in-memory
red-black-tree database. This database does not take
arguments.
</para>
<para>
Other values are possible if additional database drivers
have been linked into the server. Some sample drivers are
included
with the distribution but none are linked in by default.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dialup</command></term>
<listitem>
<para>
See the description of
<command>dialup</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>delegation-only</command></term>
<listitem>
<para>
The flag only applies to hint and stub zones. If set
to <userinput>yes</userinput>, then the zone will also be
treated as if it is also a delegation-only type zone.
</para>
<para>
See caveats in <xref linkend="root_delegation_only"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>forward</command></term>
<listitem>
<para>
Only meaningful if the zone has a forwarders
list. The <command>only</command> value causes
the lookup to fail
after trying the forwarders and getting no answer, while <command>first</command> would
allow a normal lookup to be tried.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>forwarders</command></term>
<listitem>
<para>
Used to override the list of global forwarders.
If it is not specified in a zone of type <command>forward</command>,
no forwarding is done for the zone and the global options are
not used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ixfr-base</command></term>
<listitem>
<para>
Was used in <acronym>BIND</acronym> 8 to
specify the name
of the transaction log (journal) file for dynamic update
and IXFR.
<acronym>BIND</acronym> 9 ignores the option
and constructs the name of the journal
file by appending "<filename>.jnl</filename>"
to the name of the
zone file.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ixfr-tmp-file</command></term>
<listitem>
<para>
Was an undocumented option in <acronym>BIND</acronym> 8.
Ignored in <acronym>BIND</acronym> 9.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>journal</command></term>
<listitem>
<para>
Allow the default journal's filename to be overridden.
The default is the zone's filename with "<filename>.jnl</filename>" appended.
This is applicable to <command>master</command> and <command>slave</command> zones.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-journal-size</command></term>
<listitem>
<para>
See the description of
<command>max-journal-size</command> in <xref linkend="server_resource_limits"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-in</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-time-in</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-in</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-idle-in</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-time-out</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-time-out</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>max-transfer-idle-out</command></term>
<listitem>
<para>
See the description of
<command>max-transfer-idle-out</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify</command></term>
<listitem>
<para>
See the description of
<command>notify</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-delay</command></term>
<listitem>
<para>
See the description of
<command>notify-delay</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-to-soa</command></term>
<listitem>
<para>
See the description of
<command>notify-to-soa</command> in
<xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>pubkey</command></term>
<listitem>
<para>
In <acronym>BIND</acronym> 8, this option was
intended for specifying
a public zone key for verification of signatures in DNSSEC
signed
zones when they are loaded from disk. <acronym>BIND</acronym> 9 does not verify signatures
on load and ignores the option.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>zone-statistics</command></term>
<listitem>
<para>
If <userinput>yes</userinput>, the server will keep
statistical
information for this zone, which can be dumped to the
<command>statistics-file</command> defined in
the server options.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>server-addresses</command></term>
<listitem>
<para>
Only meaningful for static-stub zones.
This is a list of IP addresses to which queries
should be sent in recursive resolution for the
zone.
A non empty list for this option will internally
configure the apex NS RR with associated glue A or
AAAA RRs.
</para>
<para>
For example, if "example.com" is configured as a
static-stub zone with 192.0.2.1 and 2001:db8::1234
in a <command>server-addresses</command> option,
the following RRs will be internally configured.
</para>
<programlisting>example.com. NS example.com.
example.com. A 192.0.2.1
example.com. AAAA 2001:db8::1234</programlisting>
<para>
These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
will initiate recursive resolution and send
queries to 192.0.2.1 and/or 2001:db8::1234.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>server-names</command></term>
<listitem>
<para>
Only meaningful for static-stub zones.
This is a list of domain names of nameservers that
act as authoritative servers of the static-stub
zone.
These names will be resolved to IP addresses when
<command>named</command> needs to send queries to
these servers.
To make this supplemental resolution successful,
these names must not be a subdomain of the origin
name of static-stub zone.
That is, when "example.net" is the origin of a
static-stub zone, "ns.example" and
"master.example.com" can be specified in the
<command>server-names</command> option, but
"ns.example.net" cannot, and will be rejected by
the configuration parser.
</para>
<para>
A non empty list for this option will internally
configure the apex NS RR with the specified names.
For example, if "example.com" is configured as a
static-stub zone with "ns1.example.net" and
"ns2.example.net"
in a <command>server-names</command> option,
the following RRs will be internally configured.
</para>
<programlisting>example.com. NS ns1.example.net.
example.com. NS ns2.example.net.
</programlisting>
<para>
These records are internally used to resolve
names under the static-stub zone.
For instance, if the server receives a query for
"www.example.com" with the RD bit on, the server
initiate recursive resolution,
resolve "ns1.example.net" and/or
"ns2.example.net" to IP addresses, and then send
queries to (one or more of) these addresses.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-validity-interval</command></term>
<listitem>
<para>
See the description of
<command>sig-validity-interval</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-nodes</command></term>
<listitem>
<para>
See the description of
<command>sig-signing-nodes</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-signatures</command></term>
<listitem>
<para>
See the description of
<command>sig-signing-signatures</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>sig-signing-type</command></term>
<listitem>
<para>
See the description of
<command>sig-signing-type</command> in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source</command></term>
<listitem>
<para>
See the description of
<command>transfer-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>transfer-source-v6</command></term>
<listitem>
<para>
See the description of
<command>transfer-source-v6</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source</command></term>
<listitem>
<para>
See the description of
<command>alt-transfer-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>alt-transfer-source-v6</command></term>
<listitem>
<para>
See the description of
<command>alt-transfer-source-v6</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>use-alt-transfer-source</command></term>
<listitem>
<para>
See the description of
<command>use-alt-transfer-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source</command></term>
<listitem>
<para>
See the description of
<command>notify-source</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>notify-source-v6</command></term>
<listitem>
<para>
See the description of
<command>notify-source-v6</command> in <xref linkend="zone_transfers"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>min-refresh-time</command></term>
<term><command>max-refresh-time</command></term>
<term><command>min-retry-time</command></term>
<term><command>max-retry-time</command></term>
<listitem>
<para>
See the description in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ixfr-from-differences</command></term>
<listitem>
<para>
See the description of
<command>ixfr-from-differences</command> in <xref linkend="boolean_options"/>.
(Note that the <command>ixfr-from-differences</command>
<userinput>master</userinput> and
<userinput>slave</userinput> choices are not
available at the zone level.)
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>key-directory</command></term>
<listitem>
<para>
See the description of
<command>key-directory</command> in <xref linkend="options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>auto-dnssec</command></term>
<listitem>
<para>
Zones configured for dynamic DNS may also use this
option to allow varying levels of automatic DNSSEC key
management. There are three possible settings:
</para>
<para>
<command>auto-dnssec allow;</command> permits
keys to be updated and the zone fully re-signed
whenever the user issues the command <command>rndc sign
<replaceable>zonename</replaceable></command>.
</para>
<para>
<command>auto-dnssec maintain;</command> includes the
above, but also automatically adjusts the zone's DNSSEC
keys on schedule, according to the keys' timing metadata
(see <xref linkend="man.dnssec-keygen"/> and
<xref linkend="man.dnssec-settime"/>). The command
<command>rndc sign
<replaceable>zonename</replaceable></command> causes
<command>named</command> to load keys from the key
repository and sign the zone with all keys that are
active.
<command>rndc loadkeys
<replaceable>zonename</replaceable></command> causes
<command>named</command> to load keys from the key
repository and schedule key maintenance events to occur
in the future, but it does not sign the full zone
immediately. Note: once keys have been loaded for a
zone the first time, the repository will be searched
for changes periodically, regardless of whether
<command>rndc loadkeys</command> is used. The recheck
interval is hard-coded to
one hour.
</para>
<para>
<command>auto-dnssec create;</command> includes the
above, but also allows <command>named</command>
to create new keys in the key repository when needed.
(NOTE: This option is not yet implemented; the syntax is
being reserved for future use.)
</para>
<para>
The default setting is <command>auto-dnssec off</command>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>multi-master</command></term>
<listitem>
<para>
See the description of <command>multi-master</command> in
<xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>masterfile-format</command></term>
<listitem>
<para>
See the description of <command>masterfile-format</command>
in <xref linkend="tuning"/>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>dnssec-secure-to-insecure</command></term>
<listitem>
<para>
See the description of
<command>dnssec-secure-to-insecure</command> in <xref linkend="boolean_options"/>.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
<sect3 id="dynamic_update_policies">
<title>Dynamic Update Policies</title>
<para><acronym>BIND</acronym> 9 supports two alternative
methods of granting clients the right to perform
dynamic updates to a zone, configured by the
<command>allow-update</command> and
<command>update-policy</command> option, respectively.
</para>
<para>
The <command>allow-update</command> clause works the
same way as in previous versions of <acronym>BIND</acronym>.
It grants given clients the permission to update any
record of any name in the zone.
</para>
<para>
The <command>update-policy</command> clause
allows more fine-grained control over what updates are
allowed. A set of rules is specified, where each rule
either grants or denies permissions for one or more
names to be updated by one or more identities. If
the dynamic update request message is signed (that is,
it includes either a TSIG or SIG(0) record), the
identity of the signer can be determined.
</para>
<para>
Rules are specified in the <command>update-policy</command>
zone option, and are only meaningful for master zones.
When the <command>update-policy</command> statement
is present, it is a configuration error for the
<command>allow-update</command> statement to be
present. The <command>update-policy</command> statement
only examines the signer of a message; the source
address is not relevant.
</para>
<para>
There is a pre-defined <command>update-policy</command>
rule which can be switched on with the command
<command>update-policy local;</command>.
Switching on this rule in a zone causes
<command>named</command> to generate a TSIG session
key and place it in a file, and to allow that key
to update the zone. (By default, the file is
<filename>/var/run/named/session.key</filename>, the key
name is "local-ddns" and the key algorithm is HMAC-SHA256,
but these values are configurable with the
<command>session-keyfile</command>,
<command>session-keyname</command> and
<command>session-keyalg</command> options, respectively).
</para>
<para>
A client running on the local system, and with appropriate
permissions, may read that file and use the key to sign update
requests. The zone's update policy will be set to allow that
key to change any record within the zone. Assuming the
key name is "local-ddns", this policy is equivalent to:
</para>
<programlisting>update-policy { grant local-ddns zonesub any; };
</programlisting>
<para>
The command <command>nsupdate -l</command> sends update
requests to localhost, and signs them using the session key.
</para>
<para>
Other rule definitions look like this:
</para>
<programlisting>
( <command>grant</command> | <command>deny</command> ) <replaceable>identity</replaceable> <replaceable>nametype</replaceable> <optional> <replaceable>name</replaceable> </optional> <optional> <replaceable>types</replaceable> </optional>
</programlisting>
<para>
Each rule grants or denies privileges. Once a message has
successfully matched a rule, the operation is immediately
granted or denied and no further rules are examined. A rule
is matched when the signer matches the identity field, the
name matches the name field in accordance with the nametype
field, and the type matches the types specified in the type
field.
</para>
<para>
No signer is required for <replaceable>tcp-self</replaceable>
or <replaceable>6to4-self</replaceable> however the standard
reverse mapping / prefix conversion must match the identity
field.
</para>
<para>
The identity field specifies a name or a wildcard
name. Normally, this is the name of the TSIG or
SIG(0) key used to sign the update request. When a
TKEY exchange has been used to create a shared secret,
the identity of the shared secret is the same as the
identity of the key used to authenticate the TKEY
exchange. TKEY is also the negotiation method used
by GSS-TSIG, which establishes an identity that is
the Kerberos principal of the client, such as
<userinput>"user@host.domain"</userinput>. When the
<replaceable>identity</replaceable> field specifies
a wildcard name, it is subject to DNS wildcard
expansion, so the rule will apply to multiple identities.
The <replaceable>identity</replaceable> field must
contain a fully-qualified domain name.
</para>
<para>
For nametypes <varname>krb5-self</varname>,
<varname>ms-self</varname>, <varname>krb5-subdomain</varname>,
and <varname>ms-subdomain</varname> the
<replaceable>identity</replaceable> field specifies
the Windows or Kerberos realm of the machine belongs to.
</para>
<para>
The <replaceable>nametype</replaceable> field has 13
values:
<varname>name</varname>, <varname>subdomain</varname>,
<varname>wildcard</varname>, <varname>self</varname>,
<varname>selfsub</varname>, <varname>selfwild</varname>,
<varname>krb5-self</varname>, <varname>ms-self</varname>,
<varname>krb5-subdomain</varname>,
<varname>ms-subdomain</varname>,
<varname>tcp-self</varname>, <varname>6to4-self</varname>,
<varname>zonesub</varname>, and <varname>external</varname>.
</para>
<informaltable>
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.819in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.681in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<varname>name</varname>
</para>
</entry> <entry colname="2">
<para>
Exact-match semantics. This rule matches
when the name being updated is identical
to the contents of the
<replaceable>name</replaceable> field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>subdomain</varname>
</para>
</entry> <entry colname="2">
<para>
This rule matches when the name being updated
is a subdomain of, or identical to, the
contents of the <replaceable>name</replaceable>
field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>zonesub</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is similar to subdomain, except that
it matches when the name being updated is a
subdomain of the zone in which the
<command>update-policy</command> statement
appears. This obviates the need to type the zone
name twice, and enables the use of a standard
<command>update-policy</command> statement in
multiple zones without modification.
</para>
<para>
When this rule is used, the
<replaceable>name</replaceable> field is omitted.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>wildcard</varname>
</para>
</entry> <entry colname="2">
<para>
The <replaceable>name</replaceable> field
is subject to DNS wildcard expansion, and
this rule matches when the name being updated
name is a valid expansion of the wildcard.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>self</varname>
</para>
</entry>
<entry colname="2">
<para>
This rule matches when the name being updated
matches the contents of the
<replaceable>identity</replaceable> field.
The <replaceable>name</replaceable> field
is ignored, but should be the same as the
<replaceable>identity</replaceable> field.
The <varname>self</varname> nametype is
most useful when allowing using one key per
name to update, where the key has the same
name as the name to be updated. The
<replaceable>identity</replaceable> would
be specified as <constant>*</constant> (an asterisk) in
this case.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>selfsub</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is similar to <varname>self</varname>
except that subdomains of <varname>self</varname>
can also be updated.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>selfwild</varname>
</para>
</entry> <entry colname="2">
<para>
This rule is similar to <varname>self</varname>
except that only subdomains of
<varname>self</varname> can be updated.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ms-self</varname>
</para>
</entry> <entry colname="2">
<para>
This rule takes a Windows machine principal
(machine$@REALM) for machine in REALM and
and converts it machine.realm allowing the machine
to update machine.realm. The REALM to be matched
is specified in the <replacable>identity</replacable>
field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>ms-subdomain</varname>
</para>
</entry> <entry colname="2">
<para>
This rule takes a Windows machine principal
(machine$@REALM) for machine in REALM and
converts it to machine.realm allowing the machine
to update subdomains of machine.realm. The REALM
to be matched is specified in the
<replacable>identity</replacable> field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>krb5-self</varname>
</para>
</entry> <entry colname="2">
<para>
This rule takes a Kerberos machine principal
(host/machine@REALM) for machine in REALM and
and converts it machine.realm allowing the machine
to update machine.realm. The REALM to be matched
is specified in the <replacable>identity</replacable>
field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>krb5-subdomain</varname>
</para>
</entry> <entry colname="2">
<para>
This rule takes a Kerberos machine principal
(host/machine@REALM) for machine in REALM and
converts it to machine.realm allowing the machine
to update subdomains of machine.realm. The REALM
to be matched is specified in the
<replacable>identity</replacable> field.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>tcp-self</varname>
</para>
</entry> <entry colname="2">
<para>
Allow updates that have been sent via TCP and
for which the standard mapping from the initiating
IP address into the IN-ADDR.ARPA and IP6.ARPA
namespaces match the name to be updated.
</para>
<note>
It is theoretically possible to spoof these TCP
sessions.
</note>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>6to4-self</varname>
</para>
</entry> <entry colname="2">
<para>
Allow the 6to4 prefix to be update by any TCP
connection from the 6to4 network or from the
corresponding IPv4 address. This is intended
to allow NS or DNAME RRsets to be added to the
reverse tree.
</para>
<note>
It is theoretically possible to spoof these TCP
sessions.
</note>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<varname>external</varname>
</para>
</entry> <entry colname="2">
<para>
This rule allows <command>named</command>
to defer the decision of whether to allow a
given update to an external daemon.
</para>
<para>
The method of communicating with the daemon is
specified in the <replaceable>identity</replaceable>
field, the format of which is
"<constant>local:</constant><replaceable>path</replaceable>",
where <replaceable>path</replaceable> is the location
of a UNIX-domain socket. (Currently, "local" is the
only supported mechanism.)
</para>
<para>
Requests to the external daemon are sent over the
UNIX-domain socket as datagrams with the following
format:
</para>
<programlisting>
Protocol version number (4 bytes, network byte order, currently 1)
Request length (4 bytes, network byte order)
Signer (null-terminated string)
Name (null-terminated string)
TCP source address (null-terminated string)
Rdata type (null-terminated string)
Key (null-terminated string)
TKEY token length (4 bytes, network byte order)
TKEY token (remainder of packet)</programlisting>
<para>
The daemon replies with a four-byte value in
network byte order, containing either 0 or 1; 0
indicates that the specified update is not
permitted, and 1 indicates that it is.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
In all cases, the <replaceable>name</replaceable>
field must specify a fully-qualified domain name.
</para>
<para>
If no types are explicitly specified, this rule matches
all types except RRSIG, NS, SOA, NSEC and NSEC3. Types
may be specified by name, including "ANY" (ANY matches
all types except NSEC and NSEC3, which can never be
updated). Note that when an attempt is made to delete
all records associated with a name, the rules are
checked for each existing record type.
</para>
</sect3>
</sect2>
</sect1>
<sect1>
<title>Zone File</title>
<sect2 id="types_of_resource_records_and_when_to_use_them">
<title>Types of Resource Records and When to Use Them</title>
<para>
This section, largely borrowed from RFC 1034, describes the
concept of a Resource Record (RR) and explains when each is used.
Since the publication of RFC 1034, several new RRs have been
identified
and implemented in the DNS. These are also included.
</para>
<sect3>
<title>Resource Records</title>
<para>
A domain name identifies a node. Each node has a set of
resource information, which may be empty. The set of resource
information associated with a particular name is composed of
separate RRs. The order of RRs in a set is not significant and
need not be preserved by name servers, resolvers, or other
parts of the DNS. However, sorting of multiple RRs is
permitted for optimization purposes, for example, to specify
that a particular nearby server be tried first. See <xref linkend="the_sortlist_statement"/> and <xref linkend="rrset_ordering"/>.
</para>
<para>
The components of a Resource Record are:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.000in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.500in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
owner name
</para>
</entry>
<entry colname="2">
<para>
The domain name where the RR is found.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
type
</para>
</entry>
<entry colname="2">
<para>
An encoded 16-bit value that specifies
the type of the resource record.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TTL
</para>
</entry>
<entry colname="2">
<para>
The time-to-live of the RR. This field
is a 32-bit integer in units of seconds, and is
primarily used by
resolvers when they cache RRs. The TTL describes how
long a RR can
be cached before it should be discarded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
class
</para>
</entry>
<entry colname="2">
<para>
An encoded 16-bit value that identifies
a protocol family or instance of a protocol.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RDATA
</para>
</entry>
<entry colname="2">
<para>
The resource data. The format of the
data is type (and sometimes class) specific.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The following are <emphasis>types</emphasis> of valid RRs:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.625in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
A
</para>
</entry>
<entry colname="2">
<para>
A host address. In the IN class, this is a
32-bit IP address. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
AAAA
</para>
</entry>
<entry colname="2">
<para>
IPv6 address. Described in RFC 1886.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
A6
</para>
</entry>
<entry colname="2">
<para>
IPv6 address. This can be a partial
address (a suffix) and an indirection to the name
where the rest of the
address (the prefix) can be found. Experimental.
Described in RFC 2874.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
AFSDB
</para>
</entry>
<entry colname="2">
<para>
Location of AFS database servers.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
APL
</para>
</entry>
<entry colname="2">
<para>
Address prefix list. Experimental.
Described in RFC 3123.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CERT
</para>
</entry>
<entry colname="2">
<para>
Holds a digital certificate.
Described in RFC 2538.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CNAME
</para>
</entry>
<entry colname="2">
<para>
Identifies the canonical name of an alias.
Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DHCID
</para>
</entry>
<entry colname="2">
<para>
Is used for identifying which DHCP client is
associated with this name. Described in RFC 4701.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DNAME
</para>
</entry>
<entry colname="2">
<para>
Replaces the domain name specified with
another name to be looked up, effectively aliasing an
entire
subtree of the domain name space rather than a single
record
as in the case of the CNAME RR.
Described in RFC 2672.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DNSKEY
</para>
</entry>
<entry colname="2">
<para>
Stores a public key associated with a signed
DNS zone. Described in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
DS
</para>
</entry>
<entry colname="2">
<para>
Stores the hash of a public key associated with a
signed DNS zone. Described in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
GPOS
</para>
</entry>
<entry colname="2">
<para>
Specifies the global position. Superseded by LOC.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
HINFO
</para>
</entry>
<entry colname="2">
<para>
Identifies the CPU and OS used by a host.
Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
IPSECKEY
</para>
</entry>
<entry colname="2">
<para>
Provides a method for storing IPsec keying material in
DNS. Described in RFC 4025.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
ISDN
</para>
</entry>
<entry colname="2">
<para>
Representation of ISDN addresses.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
KEY
</para>
</entry>
<entry colname="2">
<para>
Stores a public key associated with a
DNS name. Used in original DNSSEC; replaced
by DNSKEY in DNSSECbis, but still used with
SIG(0). Described in RFCs 2535 and 2931.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
KX
</para>
</entry>
<entry colname="2">
<para>
Identifies a key exchanger for this
DNS name. Described in RFC 2230.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
LOC
</para>
</entry>
<entry colname="2">
<para>
For storing GPS info. Described in RFC 1876.
Experimental.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
MX
</para>
</entry>
<entry colname="2">
<para>
Identifies a mail exchange for the domain with
a 16-bit preference value (lower is better)
followed by the host name of the mail exchange.
Described in RFC 974, RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NAPTR
</para>
</entry>
<entry colname="2">
<para>
Name authority pointer. Described in RFC 2915.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSAP
</para>
</entry>
<entry colname="2">
<para>
A network service access point.
Described in RFC 1706.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NS
</para>
</entry>
<entry colname="2">
<para>
The authoritative name server for the
domain. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSEC
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSECbis to securely indicate that
RRs with an owner name in a certain name interval do
not exist in
a zone and indicate what RR types are present for an
existing name.
Described in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSEC3
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSECbis to securely indicate that
RRs with an owner name in a certain name
interval do not exist in a zone and indicate
what RR types are present for an existing
name. NSEC3 differs from NSEC in that it
prevents zone enumeration but is more
computationally expensive on both the server
and the client than NSEC. Described in RFC
5155.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NSEC3PARAM
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSECbis to tell the authoritative
server which NSEC3 chains are available to use.
Described in RFC 5155.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
NXT
</para>
</entry>
<entry colname="2">
<para>
Used in DNSSEC to securely indicate that
RRs with an owner name in a certain name interval do
not exist in
a zone and indicate what RR types are present for an
existing name.
Used in original DNSSEC; replaced by NSEC in
DNSSECbis.
Described in RFC 2535.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
PTR
</para>
</entry>
<entry colname="2">
<para>
A pointer to another part of the domain
name space. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
PX
</para>
</entry>
<entry colname="2">
<para>
Provides mappings between RFC 822 and X.400
addresses. Described in RFC 2163.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RP
</para>
</entry>
<entry colname="2">
<para>
Information on persons responsible
for the domain. Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RRSIG
</para>
</entry>
<entry colname="2">
<para>
Contains DNSSECbis signature data. Described
in RFC 4034.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RT
</para>
</entry>
<entry colname="2">
<para>
Route-through binding for hosts that
do not have their own direct wide area network
addresses.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SIG
</para>
</entry>
<entry colname="2">
<para>
Contains DNSSEC signature data. Used in
original DNSSEC; replaced by RRSIG in
DNSSECbis, but still used for SIG(0).
Described in RFCs 2535 and 2931.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SOA
</para>
</entry>
<entry colname="2">
<para>
Identifies the start of a zone of authority.
Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SPF
</para>
</entry>
<entry colname="2">
<para>
Contains the Sender Policy Framework information
for a given email domain. Described in RFC 4408.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SRV
</para>
</entry>
<entry colname="2">
<para>
Information about well known network
services (replaces WKS). Described in RFC 2782.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
SSHFP
</para>
</entry>
<entry colname="2">
<para>
Provides a way to securely publish a secure shell key's
fingerprint. Described in RFC 4255.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
TXT
</para>
</entry>
<entry colname="2">
<para>
Text records. Described in RFC 1035.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
WKS
</para>
</entry>
<entry colname="2">
<para>
Information about which well known
network services, such as SMTP, that a domain
supports. Historical.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
X25
</para>
</entry>
<entry colname="2">
<para>
Representation of X.25 network addresses.
Experimental. Described in RFC 1183.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The following <emphasis>classes</emphasis> of resource records
are currently valid in the DNS:
</para>
<informaltable colsep="0" rowsep="0"><tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.625in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
IN
</para>
</entry>
<entry colname="2">
<para>
The Internet.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
CH
</para>
</entry>
<entry colname="2">
<para>
Chaosnet, a LAN protocol created at MIT in the
mid-1970s.
Rarely used for its historical purpose, but reused for
BIND's
built-in server information zones, e.g.,
<literal>version.bind</literal>.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
HS
</para>
</entry>
<entry colname="2">
<para>
Hesiod, an information service
developed by MIT's Project Athena. It is used to share
information
about various systems databases, such as users,
groups, printers
and so on.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The owner name is often implicit, rather than forming an
integral
part of the RR. For example, many name servers internally form
tree
or hash structures for the name space, and chain RRs off nodes.
The remaining RR parts are the fixed header (type, class, TTL)
which is consistent for all RRs, and a variable part (RDATA)
that
fits the needs of the resource being described.
</para>
<para>
The meaning of the TTL field is a time limit on how long an
RR can be kept in a cache. This limit does not apply to
authoritative
data in zones; it is also timed out, but by the refreshing
policies
for the zone. The TTL is assigned by the administrator for the
zone where the data originates. While short TTLs can be used to
minimize caching, and a zero TTL prohibits caching, the
realities
of Internet performance suggest that these times should be on
the
order of days for the typical host. If a change can be
anticipated,
the TTL can be reduced prior to the change to minimize
inconsistency
during the change, and then increased back to its former value
following
the change.
</para>
<para>
The data in the RDATA section of RRs is carried as a combination
of binary strings and domain names. The domain names are
frequently
used as "pointers" to other data in the DNS.
</para>
</sect3>
<sect3>
<title>Textual expression of RRs</title>
<para>
RRs are represented in binary form in the packets of the DNS
protocol, and are usually represented in highly encoded form
when
stored in a name server or resolver. In the examples provided
in
RFC 1034, a style similar to that used in master files was
employed
in order to show the contents of RRs. In this format, most RRs
are shown on a single line, although continuation lines are
possible
using parentheses.
</para>
<para>
The start of the line gives the owner of the RR. If a line
begins with a blank, then the owner is assumed to be the same as
that of the previous RR. Blank lines are often included for
readability.
</para>
<para>
Following the owner, we list the TTL, type, and class of the
RR. Class and type use the mnemonics defined above, and TTL is
an integer before the type field. In order to avoid ambiguity
in
parsing, type and class mnemonics are disjoint, TTLs are
integers,
and the type mnemonic is always last. The IN class and TTL
values
are often omitted from examples in the interests of clarity.
</para>
<para>
The resource data or RDATA section of the RR are given using
knowledge of the typical representation for the data.
</para>
<para>
For example, we might show the RRs carried in a message as:
</para>
<informaltable colsep="0" rowsep="0"><tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.381in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.020in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="2.099in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<literal>ISI.EDU.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10 VENERA.ISI.EDU.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10 VAXA.ISI.EDU</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>VENERA.ISI.EDU</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>128.9.0.32</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10.1.0.52</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>VAXA.ISI.EDU</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10.2.0.27</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>128.9.0.33</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The MX RRs have an RDATA section which consists of a 16-bit
number followed by a domain name. The address RRs use a
standard
IP address format to contain a 32-bit internet address.
</para>
<para>
The above example shows six RRs, with two RRs at each of three
domain names.
</para>
<para>
Similarly we might see:
</para>
<informaltable colsep="0" rowsep="0"><tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.491in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.067in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="2.067in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<literal>XX.LCS.MIT.EDU.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>10.0.0.44</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1"/>
<entry colname="2">
<para>
<literal>CH A</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MIT.EDU. 2420</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
This example shows two addresses for
<literal>XX.LCS.MIT.EDU</literal>, each of a different class.
</para>
</sect3>
</sect2>
<sect2>
<title>Discussion of MX Records</title>
<para>
As described above, domain servers store information as a
series of resource records, each of which contains a particular
piece of information about a given domain name (which is usually,
but not always, a host). The simplest way to think of a RR is as
a typed pair of data, a domain name matched with a relevant datum,
and stored with some additional type information to help systems
determine when the RR is relevant.
</para>
<para>
MX records are used to control delivery of email. The data
specified in the record is a priority and a domain name. The
priority
controls the order in which email delivery is attempted, with the
lowest number first. If two priorities are the same, a server is
chosen randomly. If no servers at a given priority are responding,
the mail transport agent will fall back to the next largest
priority.
Priority numbers do not have any absolute meaning — they are
relevant
only respective to other MX records for that domain name. The
domain
name given is the machine to which the mail will be delivered.
It <emphasis>must</emphasis> have an associated address record
(A or AAAA) — CNAME is not sufficient.
</para>
<para>
For a given domain, if there is both a CNAME record and an
MX record, the MX record is in error, and will be ignored.
Instead,
the mail will be delivered to the server specified in the MX
record
pointed to by the CNAME.
For example:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="5" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.708in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="0.444in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="0.444in"/>
<colspec colname="4" colnum="4" colsep="0" colwidth="0.976in"/>
<colspec colname="5" colnum="5" colsep="0" colwidth="1.553in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<literal>example.com.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>mail.example.com.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>mail2.example.com.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para/>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>MX</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>20</literal>
</para>
</entry>
<entry colname="5">
<para>
<literal>mail.backup.org.</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>mail.example.com.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10.0.0.1</literal>
</para>
</entry>
<entry colname="5">
<para/>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>mail2.example.com.</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN</literal>
</para>
</entry>
<entry colname="3">
<para>
<literal>A</literal>
</para>
</entry>
<entry colname="4">
<para>
<literal>10.0.0.2</literal>
</para>
</entry>
<entry colname="5">
<para/>
</entry>
</row>
</tbody>
</tgroup>
</informaltable><para>
Mail delivery will be attempted to <literal>mail.example.com</literal> and
<literal>mail2.example.com</literal> (in
any order), and if neither of those succeed, delivery to <literal>mail.backup.org</literal> will
be attempted.
</para>
</sect2>
<sect2 id="Setting_TTLs">
<title>Setting TTLs</title>
<para>
The time-to-live of the RR field is a 32-bit integer represented
in units of seconds, and is primarily used by resolvers when they
cache RRs. The TTL describes how long a RR can be cached before it
should be discarded. The following three types of TTL are
currently
used in a zone file.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.750in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.375in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
SOA
</para>
</entry>
<entry colname="2">
<para>
The last field in the SOA is the negative
caching TTL. This controls how long other servers will
cache no-such-domain
(NXDOMAIN) responses from you.
</para>
<para>
The maximum time for
negative caching is 3 hours (3h).
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
$TTL
</para>
</entry>
<entry colname="2">
<para>
The $TTL directive at the top of the
zone file (before the SOA) gives a default TTL for every
RR without
a specific TTL set.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
RR TTLs
</para>
</entry>
<entry colname="2">
<para>
Each RR can have a TTL as the second
field in the RR, which will control how long other
servers can cache
the it.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
All of these TTLs default to units of seconds, though units
can be explicitly specified, for example, <literal>1h30m</literal>.
</para>
</sect2>
<sect2>
<title>Inverse Mapping in IPv4</title>
<para>
Reverse name resolution (that is, translation from IP address
to name) is achieved by means of the <emphasis>in-addr.arpa</emphasis> domain
and PTR records. Entries in the in-addr.arpa domain are made in
least-to-most significant order, read left to right. This is the
opposite order to the way IP addresses are usually written. Thus,
a machine with an IP address of 10.1.2.3 would have a
corresponding
in-addr.arpa name of
3.2.1.10.in-addr.arpa. This name should have a PTR resource record
whose data field is the name of the machine or, optionally,
multiple
PTR records if the machine has more than one name. For example,
in the <optional>example.com</optional> domain:
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.125in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.000in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>
<literal>$ORIGIN</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>2.1.10.in-addr.arpa</literal>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>
<literal>3</literal>
</para>
</entry>
<entry colname="2">
<para>
<literal>IN PTR foo.example.com.</literal>
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<note>
<para>
The <command>$ORIGIN</command> lines in the examples
are for providing context to the examples only — they do not
necessarily
appear in the actual usage. They are only used here to indicate
that the example is relative to the listed origin.
</para>
</note>
</sect2>
<sect2>
<title>Other Zone File Directives</title>
<para>
The Master File Format was initially defined in RFC 1035 and
has subsequently been extended. While the Master File Format
itself
is class independent all records in a Master File must be of the
same
class.
</para>
<para>
Master File Directives include <command>$ORIGIN</command>, <command>$INCLUDE</command>,
and <command>$TTL.</command>
</para>
<sect3>
<title>The <command>@</command> (at-sign)</title>
<para>
When used in the label (or name) field, the asperand or
at-sign (@) symbol represents the current origin.
At the start of the zone file, it is the
<<varname>zone_name</varname>> (followed by
trailing dot).
</para>
</sect3>
<sect3>
<title>The <command>$ORIGIN</command> Directive</title>
<para>
Syntax: <command>$ORIGIN</command>
<replaceable>domain-name</replaceable>
<optional><replaceable>comment</replaceable></optional>
</para>
<para><command>$ORIGIN</command>
sets the domain name that will be appended to any
unqualified records. When a zone is first read in there
is an implicit <command>$ORIGIN</command>
<<varname>zone_name</varname>><command>.</command>
(followed by trailing dot).
The current <command>$ORIGIN</command> is appended to
the domain specified in the <command>$ORIGIN</command>
argument if it is not absolute.
</para>
<programlisting>
$ORIGIN example.com.
WWW CNAME MAIN-SERVER
</programlisting>
<para>
is equivalent to
</para>
<programlisting>
WWW.EXAMPLE.COM. CNAME MAIN-SERVER.EXAMPLE.COM.
</programlisting>
</sect3>
<sect3>
<title>The <command>$INCLUDE</command> Directive</title>
<para>
Syntax: <command>$INCLUDE</command>
<replaceable>filename</replaceable>
<optional>
<replaceable>origin</replaceable> </optional>
<optional> <replaceable>comment</replaceable> </optional>
</para>
<para>
Read and process the file <filename>filename</filename> as
if it were included into the file at this point. If <command>origin</command> is
specified the file is processed with <command>$ORIGIN</command> set
to that value, otherwise the current <command>$ORIGIN</command> is
used.
</para>
<para>
The origin and the current domain name
revert to the values they had prior to the <command>$INCLUDE</command> once
the file has been read.
</para>
<note>
<para>
RFC 1035 specifies that the current origin should be restored
after
an <command>$INCLUDE</command>, but it is silent
on whether the current
domain name should also be restored. BIND 9 restores both of
them.
This could be construed as a deviation from RFC 1035, a
feature, or both.
</para>
</note>
</sect3>
<sect3>
<title>The <command>$TTL</command> Directive</title>
<para>
Syntax: <command>$TTL</command>
<replaceable>default-ttl</replaceable>
<optional>
<replaceable>comment</replaceable> </optional>
</para>
<para>
Set the default Time To Live (TTL) for subsequent records
with undefined TTLs. Valid TTLs are of the range 0-2147483647
seconds.
</para>
<para><command>$TTL</command>
is defined in RFC 2308.
</para>
</sect3>
</sect2>
<sect2>
<title><acronym>BIND</acronym> Master File Extension: the <command>$GENERATE</command> Directive</title>
<para>
Syntax: <command>$GENERATE</command>
<replaceable>range</replaceable>
<replaceable>lhs</replaceable>
<optional><replaceable>ttl</replaceable></optional>
<optional><replaceable>class</replaceable></optional>
<replaceable>type</replaceable>
<replaceable>rhs</replaceable>
<optional><replaceable>comment</replaceable></optional>
</para>
<para><command>$GENERATE</command>
is used to create a series of resource records that only
differ from each other by an
iterator. <command>$GENERATE</command> can be used to
easily generate the sets of records required to support
sub /24 reverse delegations described in RFC 2317:
Classless IN-ADDR.ARPA delegation.
</para>
<programlisting>$ORIGIN 0.0.192.IN-ADDR.ARPA.
$GENERATE 1-2 @ NS SERVER$.EXAMPLE.
$GENERATE 1-127 $ CNAME $.0</programlisting>
<para>
is equivalent to
</para>
<programlisting>0.0.0.192.IN-ADDR.ARPA. NS SERVER1.EXAMPLE.
0.0.0.192.IN-ADDR.ARPA. NS SERVER2.EXAMPLE.
1.0.0.192.IN-ADDR.ARPA. CNAME 1.0.0.0.192.IN-ADDR.ARPA.
2.0.0.192.IN-ADDR.ARPA. CNAME 2.0.0.0.192.IN-ADDR.ARPA.
...
127.0.0.192.IN-ADDR.ARPA. CNAME 127.0.0.0.192.IN-ADDR.ARPA.
</programlisting>
<para>
Generate a set of A and MX records. Note the MX's right hand
side is a quoted string. The quotes will be stripped when the
right hand side is processed.
</para>
<programlisting>
$ORIGIN EXAMPLE.
$GENERATE 1-127 HOST-$ A 1.2.3.$
$GENERATE 1-127 HOST-$ MX "0 ."</programlisting>
<para>
is equivalent to
</para>
<programlisting>HOST-1.EXAMPLE. A 1.2.3.1
HOST-1.EXAMPLE. MX 0 .
HOST-2.EXAMPLE. A 1.2.3.2
HOST-2.EXAMPLE. MX 0 .
HOST-3.EXAMPLE. A 1.2.3.3
HOST-3.EXAMPLE. MX 0 .
...
HOST-127.EXAMPLE. A 1.2.3.127
HOST-127.EXAMPLE. MX 0 .
</programlisting>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="3Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="0.875in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="4.250in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para><command>range</command></para>
</entry>
<entry colname="2">
<para>
This can be one of two forms: start-stop
or start-stop/step. If the first form is used, then step
is set to
1. All of start, stop and step must be positive.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>lhs</command></para>
</entry>
<entry colname="2">
<para>This
describes the owner name of the resource records
to be created. Any single <command>$</command>
(dollar sign)
symbols within the <command>lhs</command> string
are replaced by the iterator value.
To get a $ in the output, you need to escape the
<command>$</command> using a backslash
<command>\</command>,
e.g. <command>\$</command>. The
<command>$</command> may optionally be followed
by modifiers which change the offset from the
iterator, field width and base.
Modifiers are introduced by a
<command>{</command> (left brace) immediately following the
<command>$</command> as
<command>${offset[,width[,base]]}</command>.
For example, <command>${-20,3,d}</command>
subtracts 20 from the current value, prints the
result as a decimal in a zero-padded field of
width 3.
Available output forms are decimal
(<command>d</command>), octal
(<command>o</command>), hexadecimal
(<command>x</command> or <command>X</command>
for uppercase) and nibble
(<command>n</command> or <command>N</command>\
for uppercase). The default modifier is
<command>${0,0,d}</command>. If the
<command>lhs</command> is not absolute, the
current <command>$ORIGIN</command> is appended
to the name.
</para>
<para>
In nibble mode the value will be treated as
if it was a reversed hexadecimal string
with each hexadecimal digit as a separate
label. The width field includes the label
separator.
</para>
<para>
For compatibility with earlier versions,
<command>$$</command> is still recognized as
indicating a literal $ in the output.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ttl</command></para>
</entry>
<entry colname="2">
<para>
Specifies the time-to-live of the generated records. If
not specified this will be inherited using the
normal TTL inheritance rules.
</para>
<para><command>class</command>
and <command>ttl</command> can be
entered in either order.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>class</command></para>
</entry>
<entry colname="2">
<para>
Specifies the class of the generated records.
This must match the zone class if it is
specified.
</para>
<para><command>class</command>
and <command>ttl</command> can be
entered in either order.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>type</command></para>
</entry>
<entry colname="2">
<para>
Any valid type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>rhs</command></para>
</entry>
<entry colname="2">
<para>
<command>rhs</command>, optionally, quoted string.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
The <command>$GENERATE</command> directive is a <acronym>BIND</acronym> extension
and not part of the standard zone file format.
</para>
<para>
BIND 8 does not support the optional TTL and CLASS fields.
</para>
</sect2>
<sect2 id="zonefile_format">
<title>Additional File Formats</title>
<para>
In addition to the standard textual format, BIND 9
supports the ability to read or dump to zone files in
other formats. The <constant>raw</constant> format is
currently available as an additional format. It is a
binary format representing BIND 9's internal data
structure directly, thereby remarkably improving the
loading time.
</para>
<para>
For a primary server, a zone file in the
<constant>raw</constant> format is expected to be
generated from a textual zone file by the
<command>named-compilezone</command> command. For a
secondary server or for a dynamic zone, it is automatically
generated (if this format is specified by the
<command>masterfile-format</command> option) when
<command>named</command> dumps the zone contents after
zone transfer or when applying prior updates.
</para>
<para>
If a zone file in a binary format needs manual modification,
it first must be converted to a textual form by the
<command>named-compilezone</command> command. All
necessary modification should go to the text file, which
should then be converted to the binary form by the
<command>named-compilezone</command> command again.
</para>
<para>
Although the <constant>raw</constant> format uses the
network byte order and avoids architecture-dependent
data alignment so that it is as much portable as
possible, it is primarily expected to be used inside
the same single system. In order to export a zone
file in the <constant>raw</constant> format or make a
portable backup of the file, it is recommended to
convert the file to the standard textual representation.
</para>
</sect2>
</sect1>
<sect1 id="statistics">
<title>BIND9 Statistics</title>
<para>
<acronym>BIND</acronym> 9 maintains lots of statistics
information and provides several interfaces for users to
get access to the statistics.
The available statistics include all statistics counters
that were available in <acronym>BIND</acronym> 8 and
are meaningful in <acronym>BIND</acronym> 9,
and other information that is considered useful.
</para>
<para>
The statistics information is categorized into the following
sections.
</para>
<informaltable frame="all">
<tgroup cols="2">
<colspec colname="1" colnum="1" colsep="0" colwidth="3.300in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="2.625in"/>
<tbody>
<row rowsep="0">
<entry colname="1">
<para>Incoming Requests</para>
</entry>
<entry colname="2">
<para>
The number of incoming DNS requests for each OPCODE.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Incoming Queries</para>
</entry>
<entry colname="2">
<para>
The number of incoming queries for each RR type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Outgoing Queries</para>
</entry>
<entry colname="2">
<para>
The number of outgoing queries for each RR
type sent from the internal resolver.
Maintained per view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Name Server Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters about incoming request processing.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Zone Maintenance Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters regarding zone maintenance
operations such as zone transfers.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Resolver Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters about name resolution
performed in the internal resolver.
Maintained per view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Cache DB RRsets</para>
</entry>
<entry colname="2">
<para>
The number of RRsets per RR type and nonexistent
names stored in the cache database.
If the exclamation mark (!) is printed for a RR
type, it means that particular type of RRset is
known to be nonexistent (this is also known as
"NXRRSET").
Maintained per view.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para>Socket I/O Statistics</para>
</entry>
<entry colname="2">
<para>
Statistics counters about network related events.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>
A subset of Name Server Statistics is collected and shown
per zone for which the server has the authority when
<command>zone-statistics</command> is set to
<userinput>yes</userinput>.
These statistics counters are shown with their zone and view
names.
In some cases the view names are omitted for the default view.
</para>
<para>
There are currently two user interfaces to get access to the
statistics.
One is in the plain text format dumped to the file specified
by the <command>statistics-file</command> configuration option.
The other is remotely accessible via a statistics channel
when the <command>statistics-channels</command> statement
is specified in the configuration file
(see <xref linkend="statschannels"/>.)
</para>
<sect3 id="statsfile">
<title>The Statistics File</title>
<para>
The text format statistics dump begins with a line, like:
</para>
<para>
<command>+++ Statistics Dump +++ (973798949)</command>
</para>
<para>
The number in parentheses is a standard
Unix-style timestamp, measured as seconds since January 1, 1970.
Following
that line is a set of statistics information, which is categorized
as described above.
Each section begins with a line, like:
</para>
<para>
<command>++ Name Server Statistics ++</command>
</para>
<para>
Each section consists of lines, each containing the statistics
counter value followed by its textual description.
See below for available counters.
For brevity, counters that have a value of 0 are not shown
in the statistics file.
</para>
<para>
The statistics dump ends with the line where the
number is identical to the number in the beginning line; for example:
</para>
<para>
<command>--- Statistics Dump --- (973798949)</command>
</para>
</sect3>
<sect2 id="statistics_counters">
<title>Statistics Counters</title>
<para>
The following tables summarize statistics counters that
<acronym>BIND</acronym> 9 provides.
For each row of the tables, the leftmost column is the
abbreviated symbol name of that counter.
These symbols are shown in the statistics information
accessed via an HTTP statistics channel.
The rightmost column gives the description of the counter,
which is also shown in the statistics file
(but, in this document, possibly with slight modification
for better readability).
Additional notes may also be provided in this column.
When a middle column exists between these two columns,
it gives the corresponding counter name of the
<acronym>BIND</acronym> 8 statistics, if applicable.
</para>
<sect3>
<title>Name Server Statistics Counters</title>
<informaltable colsep="0" rowsep="0">
<tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>BIND8 Symbol</emphasis>
</para>
</entry>
<entry colname="3">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Requestv4</command></para>
</entry>
<entry colname="2">
<para><command>RQ</command></para>
</entry>
<entry colname="3">
<para>
IPv4 requests received.
Note: this also counts non query requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Requestv6</command></para>
</entry>
<entry colname="2">
<para><command>RQ</command></para>
</entry>
<entry colname="3">
<para>
IPv6 requests received.
Note: this also counts non query requests.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqEdns0</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Requests with EDNS(0) received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqBadEDNSVer</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Requests with unsupported EDNS version received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqTSIG</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Requests with TSIG received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqSIG0</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Requests with SIG(0) received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqBadSIG</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Requests with invalid (TSIG or SIG(0)) signature.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ReqTCP</command></para>
</entry>
<entry colname="2">
<para><command>RTCP</command></para>
</entry>
<entry colname="3">
<para>
TCP requests received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>AuthQryRej</command></para>
</entry>
<entry colname="2">
<para><command>RUQ</command></para>
</entry>
<entry colname="3">
<para>
Authoritative (non recursive) queries rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RecQryRej</command></para>
</entry>
<entry colname="2">
<para><command>RURQ</command></para>
</entry>
<entry colname="3">
<para>
Recursive queries rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrRej</command></para>
</entry>
<entry colname="2">
<para><command>RUXFR</command></para>
</entry>
<entry colname="3">
<para>
Zone transfer requests rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateRej</command></para>
</entry>
<entry colname="2">
<para><command>RUUpd</command></para>
</entry>
<entry colname="3">
<para>
Dynamic update requests rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Response</command></para>
</entry>
<entry colname="2">
<para><command>SAns</command></para>
</entry>
<entry colname="3">
<para>
Responses sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespTruncated</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Truncated responses sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespEDNS0</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Responses with EDNS(0) sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespTSIG</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Responses with TSIG sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RespSIG0</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Responses with SIG(0) sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QrySuccess</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in a successful answer.
This means the query which returns a NOERROR response
with at least one answer RR.
This corresponds to the
<command>success</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryAuthAns</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in authoritative answer.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNoauthAns</command></para>
</entry>
<entry colname="2">
<para><command>SNaAns</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in non authoritative answer.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryReferral</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in referral answer.
This corresponds to the
<command>referral</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNxrrset</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in NOERROR responses with no data.
This corresponds to the
<command>nxrrset</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QrySERVFAIL</command></para>
</entry>
<entry colname="2">
<para><command>SFail</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in SERVFAIL.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryFORMERR</command></para>
</entry>
<entry colname="2">
<para><command>SFErr</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in FORMERR.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryNXDOMAIN</command></para>
</entry>
<entry colname="2">
<para><command>SNXD</command></para>
</entry>
<entry colname="3">
<para>
Queries resulted in NXDOMAIN.
This corresponds to the
<command>nxdomain</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryRecursion</command></para>
</entry>
<entry colname="2">
<para><command>RFwdQ</command></para>
</entry>
<entry colname="3">
<para>
Queries which caused the server
to perform recursion in order to find the final answer.
This corresponds to the
<command>recursion</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryDuplicate</command></para>
</entry>
<entry colname="2">
<para><command>RDupQ</command></para>
</entry>
<entry colname="3">
<para>
Queries which the server attempted to
recurse but discovered an existing query with the same
IP address, port, query ID, name, type and class
already being processed.
This corresponds to the
<command>duplicate</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryDropped</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Recursive queries for which the server
discovered an excessive number of existing
recursive queries for the same name, type and
class and were subsequently dropped.
This is the number of dropped queries due to
the reason explained with the
<command>clients-per-query</command>
and
<command>max-clients-per-query</command>
options
(see the description about
<xref linkend="clients-per-query"/>.)
This corresponds to the
<command>dropped</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryFailure</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Other query failures.
This corresponds to the
<command>failure</command> counter
of previous versions of
<acronym>BIND</acronym> 9.
Note: this counter is provided mainly for
backward compatibility with the previous versions.
Normally a more fine-grained counters such as
<command>AuthQryRej</command> and
<command>RecQryRej</command>
that would also fall into this counter are provided,
and so this counter would not be of much
interest in practice.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrReqDone</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Requested zone transfers completed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateReqFwd</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Update requests forwarded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateRespFwd</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Update responses forwarded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateFwdFail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Dynamic update forward failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateDone</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Dynamic updates completed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateFail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Dynamic updates failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>UpdateBadPrereq</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Dynamic updates rejected due to prerequisite failure.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>Zone Maintenance Statistics Counters</title>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyOutv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 notifies sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyOutv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 notifies sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyInv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 notifies received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyInv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 notifies received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NotifyRej</command></para>
</entry>
<entry colname="2">
<para>
Incoming notifies rejected.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SOAOutv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 SOA queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SOAOutv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 SOA queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>AXFRReqv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 AXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>AXFRReqv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 AXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>IXFRReqv4</command></para>
</entry>
<entry colname="2">
<para>
IPv4 IXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>IXFRReqv6</command></para>
</entry>
<entry colname="2">
<para>
IPv6 IXFR requested.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrSuccess</command></para>
</entry>
<entry colname="2">
<para>
Zone transfer requests succeeded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>XfrFail</command></para>
</entry>
<entry colname="2">
<para>
Zone transfer requests failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RateDropped</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Responses dropped by rate limits.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>RateSlipped</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Responses truncated by rate limits.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>Resolver Statistics Counters</title>
<informaltable colsep="0" rowsep="0">
<tgroup cols="3" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="1.150in"/>
<colspec colname="3" colnum="3" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>BIND8 Symbol</emphasis>
</para>
</entry>
<entry colname="3">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Queryv4</command></para>
</entry>
<entry colname="2">
<para><command>SFwdQ</command></para>
</entry>
<entry colname="3">
<para>
IPv4 queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Queryv6</command></para>
</entry>
<entry colname="2">
<para><command>SFwdQ</command></para>
</entry>
<entry colname="3">
<para>
IPv6 queries sent.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Responsev4</command></para>
</entry>
<entry colname="2">
<para><command>RR</command></para>
</entry>
<entry colname="3">
<para>
IPv4 responses received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Responsev6</command></para>
</entry>
<entry colname="2">
<para><command>RR</command></para>
</entry>
<entry colname="3">
<para>
IPv6 responses received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>NXDOMAIN</command></para>
</entry>
<entry colname="2">
<para><command>RNXD</command></para>
</entry>
<entry colname="3">
<para>
NXDOMAIN received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>SERVFAIL</command></para>
</entry>
<entry colname="2">
<para><command>RFail</command></para>
</entry>
<entry colname="3">
<para>
SERVFAIL received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>FORMERR</command></para>
</entry>
<entry colname="2">
<para><command>RFErr</command></para>
</entry>
<entry colname="3">
<para>
FORMERR received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>OtherError</command></para>
</entry>
<entry colname="2">
<para><command>RErr</command></para>
</entry>
<entry colname="3">
<para>
Other errors received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>EDNS0Fail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
EDNS(0) query failures.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Mismatch</command></para>
</entry>
<entry colname="2">
<para><command>RDupR</command></para>
</entry>
<entry colname="3">
<para>
Mismatch responses received.
The DNS ID, response's source address,
and/or the response's source port does not
match what was expected.
(The port must be 53 or as defined by
the <command>port</command> option.)
This may be an indication of a cache
poisoning attempt.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Truncated</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Truncated responses received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Lame</command></para>
</entry>
<entry colname="2">
<para><command>RLame</command></para>
</entry>
<entry colname="3">
<para>
Lame delegations received.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>Retry</command></para>
</entry>
<entry colname="2">
<para><command>SDupQ</command></para>
</entry>
<entry colname="3">
<para>
Query retries performed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QueryAbort</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Queries aborted due to quota control.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QuerySockFail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Failures in opening query sockets.
One common reason for such failures is a
failure of opening a new socket due to a
limitation on file descriptors.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QueryTimeout</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Query timeouts.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv4</command></para>
</entry>
<entry colname="2">
<para><command>SSysQ</command></para>
</entry>
<entry colname="3">
<para>
IPv4 NS address fetches invoked.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv6</command></para>
</entry>
<entry colname="2">
<para><command>SSysQ</command></para>
</entry>
<entry colname="3">
<para>
IPv6 NS address fetches invoked.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv4Fail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
IPv4 NS address fetch failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>GlueFetchv6Fail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
IPv6 NS address fetch failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValAttempt</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation attempted.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValOk</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation succeeded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValNegOk</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation on negative information succeeded.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>ValFail</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
DNSSEC validation failed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command>QryRTTnn</command></para>
</entry>
<entry colname="2">
<para><command></command></para>
</entry>
<entry colname="3">
<para>
Frequency table on round trip times (RTTs) of
queries.
Each <command>nn</command> specifies the corresponding
frequency.
In the sequence of
<command>nn_1</command>,
<command>nn_2</command>,
...,
<command>nn_m</command>,
the value of <command>nn_i</command> is the
number of queries whose RTTs are between
<command>nn_(i-1)</command> (inclusive) and
<command>nn_i</command> (exclusive) milliseconds.
For the sake of convenience we define
<command>nn_0</command> to be 0.
The last entry should be represented as
<command>nn_m+</command>, which means the
number of queries whose RTTs are equal to or over
<command>nn_m</command> milliseconds.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>Socket I/O Statistics Counters</title>
<para>
Socket I/O statistics counters are defined per socket
types, which are
<command>UDP4</command> (UDP/IPv4),
<command>UDP6</command> (UDP/IPv6),
<command>TCP4</command> (TCP/IPv4),
<command>TCP6</command> (TCP/IPv6),
<command>Unix</command> (Unix Domain), and
<command>FDwatch</command> (sockets opened outside the
socket module).
In the following table <command><TYPE></command>
represents a socket type.
Not all counters are available for all socket types;
exceptions are noted in the description field.
</para>
<informaltable colsep="0" rowsep="0">
<tgroup cols="2" colsep="0" rowsep="0" tgroupstyle="4Level-table">
<colspec colname="1" colnum="1" colsep="0" colwidth="1.150in"/>
<colspec colname="2" colnum="2" colsep="0" colwidth="3.350in"/>
<tbody>
<row>
<entry colname="1">
<para>
<emphasis>Symbol</emphasis>
</para>
</entry>
<entry colname="2">
<para>
<emphasis>Description</emphasis>
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>Open</command></para>
</entry>
<entry colname="2">
<para>
Sockets opened successfully.
This counter is not applicable to the
<command>FDwatch</command> type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>OpenFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of opening sockets.
This counter is not applicable to the
<command>FDwatch</command> type.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>Close</command></para>
</entry>
<entry colname="2">
<para>
Sockets closed.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>BindFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of binding sockets.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>ConnFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of connecting sockets.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>Conn</command></para>
</entry>
<entry colname="2">
<para>
Connections established successfully.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>AcceptFail</command></para>
</entry>
<entry colname="2">
<para>
Failures of accepting incoming connection requests.
This counter is not applicable to the
<command>UDP</command> and
<command>FDwatch</command> types.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>Accept</command></para>
</entry>
<entry colname="2">
<para>
Incoming connections successfully accepted.
This counter is not applicable to the
<command>UDP</command> and
<command>FDwatch</command> types.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>SendErr</command></para>
</entry>
<entry colname="2">
<para>
Errors in socket send operations.
This counter corresponds
to <command>SErr</command> counter of
<command>BIND</command> 8.
</para>
</entry>
</row>
<row rowsep="0">
<entry colname="1">
<para><command><TYPE>RecvErr</command></para>
</entry>
<entry colname="2">
<para>
Errors in socket receive operations.
This includes errors of send operations on a
connected UDP socket notified by an ICMP error
message.
</para>
</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect3>
<sect3>
<title>Compatibility with <emphasis>BIND</emphasis> 8 Counters</title>
<para>
Most statistics counters that were available
in <command>BIND</command> 8 are also supported in
<command>BIND</command> 9 as shown in the above tables.
Here are notes about other counters that do not appear
in these tables.
</para>
<variablelist>
<varlistentry>
<term><command>RFwdR,SFwdR</command></term>
<listitem>
<para>
These counters are not supported
because <command>BIND</command> 9 does not adopt
the notion of <emphasis>forwarding</emphasis>
as <command>BIND</command> 8 did.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RAXFR</command></term>
<listitem>
<para>
This counter is accessible in the Incoming Queries section.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>RIQ</command></term>
<listitem>
<para>
This counter is accessible in the Incoming Requests section.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>ROpts</command></term>
<listitem>
<para>
This counter is not supported
because <command>BIND</command> 9 does not care
about IP options in the first place.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect3>
</sect2>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch07">
<title><acronym>BIND</acronym> 9 Security Considerations</title>
<sect1 id="Access_Control_Lists">
<title>Access Control Lists</title>
<para>
Access Control Lists (ACLs) are address match lists that
you can set up and nickname for future use in <command>allow-notify</command>,
<command>allow-query</command>, <command>allow-query-on</command>,
<command>allow-recursion</command>, <command>allow-recursion-on</command>,
<command>blackhole</command>, <command>allow-transfer</command>,
etc.
</para>
<para>
Using ACLs allows you to have finer control over who can access
your name server, without cluttering up your config files with huge
lists of IP addresses.
</para>
<para>
It is a <emphasis>good idea</emphasis> to use ACLs, and to
control access to your server. Limiting access to your server by
outside parties can help prevent spoofing and denial of service (DoS) attacks against
your server.
</para>
<para>
Here is an example of how to properly apply ACLs:
</para>
<programlisting>
// Set up an ACL named "bogusnets" that will block
// RFC1918 space and some reserved space, which is
// commonly used in spoofing attacks.
acl bogusnets {
0.0.0.0/8; 192.0.2.0/24; 224.0.0.0/3;
10.0.0.0/8; 172.16.0.0/12; 192.168.0.0/16;
};
// Set up an ACL called our-nets. Replace this with the
// real IP numbers.
acl our-nets { x.x.x.x/24; x.x.x.x/21; };
options {
...
...
allow-query { our-nets; };
allow-recursion { our-nets; };
...
blackhole { bogusnets; };
...
};
zone "example.com" {
type master;
file "m/example.com";
allow-query { any; };
};
</programlisting>
<para>
This allows recursive queries of the server from the outside
unless recursion has been previously disabled.
</para>
<para>
For more information on how to use ACLs to protect your server,
see the <emphasis>AUSCERT</emphasis> advisory at:
</para>
<para>
<ulink url="ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos"
>ftp://ftp.auscert.org.au/pub/auscert/advisory/AL-1999.004.dns_dos</ulink>
</para>
</sect1>
<sect1>
<title><command>Chroot</command> and <command>Setuid</command></title>
<para>
On UNIX servers, it is possible to run <acronym>BIND</acronym>
in a <emphasis>chrooted</emphasis> environment (using
the <command>chroot()</command> function) by specifying
the "<option>-t</option>" option for <command>named</command>.
This can help improve system security by placing
<acronym>BIND</acronym> in a "sandbox", which will limit
the damage done if a server is compromised.
</para>
<para>
Another useful feature in the UNIX version of <acronym>BIND</acronym> is the
ability to run the daemon as an unprivileged user ( <option>-u</option> <replaceable>user</replaceable> ).
We suggest running as an unprivileged user when using the <command>chroot</command> feature.
</para>
<para>
Here is an example command line to load <acronym>BIND</acronym> in a <command>chroot</command> sandbox,
<command>/var/named</command>, and to run <command>named</command> <command>setuid</command> to
user 202:
</para>
<para>
<userinput>/usr/local/sbin/named -u 202 -t /var/named</userinput>
</para>
<sect2>
<title>The <command>chroot</command> Environment</title>
<para>
In order for a <command>chroot</command> environment
to
work properly in a particular directory
(for example, <filename>/var/named</filename>),
you will need to set up an environment that includes everything
<acronym>BIND</acronym> needs to run.
From <acronym>BIND</acronym>'s point of view, <filename>/var/named</filename> is
the root of the filesystem. You will need to adjust the values of
options like
like <command>directory</command> and <command>pid-file</command> to account
for this.
</para>
<para>
Unlike with earlier versions of BIND, you typically will
<emphasis>not</emphasis> need to compile <command>named</command>
statically nor install shared libraries under the new root.
However, depending on your operating system, you may need
to set up things like
<filename>/dev/zero</filename>,
<filename>/dev/random</filename>,
<filename>/dev/log</filename>, and
<filename>/etc/localtime</filename>.
</para>
</sect2>
<sect2>
<title>Using the <command>setuid</command> Function</title>
<para>
Prior to running the <command>named</command> daemon,
use
the <command>touch</command> utility (to change file
access and
modification times) or the <command>chown</command>
utility (to
set the user id and/or group id) on files
to which you want <acronym>BIND</acronym>
to write.
</para>
<note>
Note that if the <command>named</command> daemon is running as an
unprivileged user, it will not be able to bind to new restricted
ports if the server is reloaded.
</note>
</sect2>
</sect1>
<sect1 id="dynamic_update_security">
<title>Dynamic Update Security</title>
<para>
Access to the dynamic
update facility should be strictly limited. In earlier versions of
<acronym>BIND</acronym>, the only way to do this was
based on the IP
address of the host requesting the update, by listing an IP address
or
network prefix in the <command>allow-update</command>
zone option.
This method is insecure since the source address of the update UDP
packet
is easily forged. Also note that if the IP addresses allowed by the
<command>allow-update</command> option include the
address of a slave
server which performs forwarding of dynamic updates, the master can
be
trivially attacked by sending the update to the slave, which will
forward it to the master with its own source IP address causing the
master to approve it without question.
</para>
<para>
For these reasons, we strongly recommend that updates be
cryptographically authenticated by means of transaction signatures
(TSIG). That is, the <command>allow-update</command>
option should
list only TSIG key names, not IP addresses or network
prefixes. Alternatively, the new <command>update-policy</command>
option can be used.
</para>
<para>
Some sites choose to keep all dynamically-updated DNS data
in a subdomain and delegate that subdomain to a separate zone. This
way, the top-level zone containing critical data such as the IP
addresses
of public web and mail servers need not allow dynamic update at
all.
</para>
</sect1>
</chapter>
<chapter id="Bv9ARM.ch08">
<title>Troubleshooting</title>
<sect1>
<title>Common Problems</title>
<sect2>
<title>It's not working; how can I figure out what's wrong?</title>
<para>
The best solution to solving installation and
configuration issues is to take preventative measures by setting
up logging files beforehand. The log files provide a
source of hints and information that can be used to figure out
what went wrong and how to fix the problem.
</para>
</sect2>
</sect1>
<sect1>
<title>Incrementing and Changing the Serial Number</title>
<para>
Zone serial numbers are just numbers — they aren't
date related. A lot of people set them to a number that
represents a date, usually of the form YYYYMMDDRR.
Occasionally they will make a mistake and set them to a
"date in the future" then try to correct them by setting
them to the "current date". This causes problems because
serial numbers are used to indicate that a zone has been
updated. If the serial number on the slave server is
lower than the serial number on the master, the slave
server will attempt to update its copy of the zone.
</para>
<para>
Setting the serial number to a lower number on the master
server than the slave server means that the slave will not perform
updates to its copy of the zone.
</para>
<para>
The solution to this is to add 2147483647 (2^31-1) to the
number, reload the zone and make sure all slaves have updated to
the new zone serial number, then reset the number to what you want
it to be, and reload the zone again.
</para>
</sect1>
<sect1>
<title>Where Can I Get Help?</title>
<para>
The Internet Systems Consortium
(<acronym>ISC</acronym>) offers a wide range
of support and service agreements for <acronym>BIND</acronym> and <acronym>DHCP</acronym> servers. Four
levels of premium support are available and each level includes
support for all <acronym>ISC</acronym> programs,
significant discounts on products
and training, and a recognized priority on bug fixes and
non-funded feature requests. In addition, <acronym>ISC</acronym> offers a standard
support agreement package which includes services ranging from bug
fix announcements to remote support. It also includes training in
<acronym>BIND</acronym> and <acronym>DHCP</acronym>.
</para>
<para>
To discuss arrangements for support, contact
<ulink url="mailto:info@isc.org">info@isc.org</ulink> or visit the
<acronym>ISC</acronym> web page at
<ulink url="http://www.isc.org/services/support/"
>http://www.isc.org/services/support/</ulink>
to read more.
</para>
</sect1>
</chapter>
<appendix id="Bv9ARM.ch09">
<title>Appendices</title>
<sect1>
<title>Acknowledgments</title>
<sect2 id="historical_dns_information">
<title>A Brief History of the <acronym>DNS</acronym> and <acronym>BIND</acronym></title>
<para>
Although the "official" beginning of the Domain Name
System occurred in 1984 with the publication of RFC 920, the
core of the new system was described in 1983 in RFCs 882 and
883. From 1984 to 1987, the ARPAnet (the precursor to today's
Internet) became a testbed of experimentation for developing the
new naming/addressing scheme in a rapidly expanding,
operational network environment. New RFCs were written and
published in 1987 that modified the original documents to
incorporate improvements based on the working model. RFC 1034,
"Domain Names-Concepts and Facilities", and RFC 1035, "Domain
Names-Implementation and Specification" were published and
became the standards upon which all <acronym>DNS</acronym> implementations are
built.
</para>
<para>
The first working domain name server, called "Jeeves", was
written in 1983-84 by Paul Mockapetris for operation on DEC
Tops-20
machines located at the University of Southern California's
Information
Sciences Institute (USC-ISI) and SRI International's Network
Information
Center (SRI-NIC). A <acronym>DNS</acronym> server for
Unix machines, the Berkeley Internet
Name Domain (<acronym>BIND</acronym>) package, was
written soon after by a group of
graduate students at the University of California at Berkeley
under
a grant from the US Defense Advanced Research Projects
Administration
(DARPA).
</para>
<para>
Versions of <acronym>BIND</acronym> through
4.8.3 were maintained by the Computer
Systems Research Group (CSRG) at UC Berkeley. Douglas Terry, Mark
Painter, David Riggle and Songnian Zhou made up the initial <acronym>BIND</acronym>
project team. After that, additional work on the software package
was done by Ralph Campbell. Kevin Dunlap, a Digital Equipment
Corporation
employee on loan to the CSRG, worked on <acronym>BIND</acronym> for 2 years, from 1985
to 1987. Many other people also contributed to <acronym>BIND</acronym> development
during that time: Doug Kingston, Craig Partridge, Smoot
Carl-Mitchell,
Mike Muuss, Jim Bloom and Mike Schwartz. <acronym>BIND</acronym> maintenance was subsequently
handled by Mike Karels and Øivind Kure.
</para>
<para>
<acronym>BIND</acronym> versions 4.9 and 4.9.1 were
released by Digital Equipment
Corporation (now Compaq Computer Corporation). Paul Vixie, then
a DEC employee, became <acronym>BIND</acronym>'s
primary caretaker. He was assisted
by Phil Almquist, Robert Elz, Alan Barrett, Paul Albitz, Bryan
Beecher, Andrew
Partan, Andy Cherenson, Tom Limoncelli, Berthold Paffrath, Fuat
Baran, Anant Kumar, Art Harkin, Win Treese, Don Lewis, Christophe
Wolfhugel, and others.
</para>
<para>
In 1994, <acronym>BIND</acronym> version 4.9.2 was sponsored by
Vixie Enterprises. Paul
Vixie became <acronym>BIND</acronym>'s principal
architect/programmer.
</para>
<para>
<acronym>BIND</acronym> versions from 4.9.3 onward
have been developed and maintained
by the Internet Systems Consortium and its predecessor,
the Internet Software Consortium, with support being provided
by ISC's sponsors.
</para>
<para>
As co-architects/programmers, Bob Halley and
Paul Vixie released the first production-ready version of
<acronym>BIND</acronym> version 8 in May 1997.
</para>
<para>
BIND version 9 was released in September 2000 and is a
major rewrite of nearly all aspects of the underlying
BIND architecture.
</para>
<para>
BIND versions 4 and 8 are officially deprecated.
No additional development is done
on BIND version 4 or BIND version 8.
</para>
<para>
<acronym>BIND</acronym> development work is made
possible today by the sponsorship
of several corporations, and by the tireless work efforts of
numerous individuals.
</para>
</sect2>
</sect1>
<sect1>
<title>General <acronym>DNS</acronym> Reference Information</title>
<sect2 id="ipv6addresses">
<title>IPv6 addresses (AAAA)</title>
<para>
IPv6 addresses are 128-bit identifiers for interfaces and
sets of interfaces which were introduced in the <acronym>DNS</acronym> to facilitate
scalable Internet routing. There are three types of addresses: <emphasis>Unicast</emphasis>,
an identifier for a single interface;
<emphasis>Anycast</emphasis>,
an identifier for a set of interfaces; and <emphasis>Multicast</emphasis>,
an identifier for a set of interfaces. Here we describe the global
Unicast address scheme. For more information, see RFC 3587,
"Global Unicast Address Format."
</para>
<para>
IPv6 unicast addresses consist of a
<emphasis>global routing prefix</emphasis>, a
<emphasis>subnet identifier</emphasis>, and an
<emphasis>interface identifier</emphasis>.
</para>
<para>
The global routing prefix is provided by the
upstream provider or ISP, and (roughly) corresponds to the
IPv4 <emphasis>network</emphasis> section
of the address range.
The subnet identifier is for local subnetting, much the
same as subnetting an
IPv4 /16 network into /24 subnets.
The interface identifier is the address of an individual
interface on a given network; in IPv6, addresses belong to
interfaces rather than to machines.
</para>
<para>
The subnetting capability of IPv6 is much more flexible than
that of IPv4: subnetting can be carried out on bit boundaries,
in much the same way as Classless InterDomain Routing
(CIDR), and the DNS PTR representation ("nibble" format)
makes setting up reverse zones easier.
</para>
<para>
The Interface Identifier must be unique on the local link,
and is usually generated automatically by the IPv6
implementation, although it is usually possible to
override the default setting if necessary. A typical IPv6
address might look like:
<command>2001:db8:201:9:a00:20ff:fe81:2b32</command>
</para>
<para>
IPv6 address specifications often contain long strings
of zeros, so the architects have included a shorthand for
specifying
them. The double colon (`::') indicates the longest possible
string
of zeros that can fit, and can be used only once in an address.
</para>
</sect2>
</sect1>
<sect1 id="bibliography">
<title>Bibliography (and Suggested Reading)</title>
<sect2 id="rfcs">
<title>Request for Comments (RFCs)</title>
<para>
Specification documents for the Internet protocol suite, including
the <acronym>DNS</acronym>, are published as part of
the Request for Comments (RFCs)
series of technical notes. The standards themselves are defined
by the Internet Engineering Task Force (IETF) and the Internet
Engineering Steering Group (IESG). RFCs can be obtained online via FTP at:
</para>
<para>
<ulink url="ftp://www.isi.edu/in-notes/">
ftp://www.isi.edu/in-notes/RFC<replaceable>xxxx</replaceable>.txt
</ulink>
</para>
<para>
(where <replaceable>xxxx</replaceable> is
the number of the RFC). RFCs are also available via the Web at:
</para>
<para>
<ulink url="http://www.ietf.org/rfc/"
>http://www.ietf.org/rfc/</ulink>.
</para>
<bibliography>
<bibliodiv>
<!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
<title>Standards</title>
<biblioentry>
<abbrev>RFC974</abbrev>
<author>
<surname>Partridge</surname>
<firstname>C.</firstname>
</author>
<title>Mail Routing and the Domain System</title>
<pubdate>January 1986</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1034</abbrev>
<author>
<surname>Mockapetris</surname>
<firstname>P.V.</firstname>
</author>
<title>Domain Names — Concepts and Facilities</title>
<pubdate>November 1987</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1035</abbrev>
<author>
<surname>Mockapetris</surname>
<firstname>P. V.</firstname>
</author> <title>Domain Names — Implementation and
Specification</title>
<pubdate>November 1987</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv id="proposed_standards" xreflabel="Proposed Standards">
<title>Proposed Standards</title>
<!-- one of (BIBLIOENTRY BIBLIOMIXED) -->
<biblioentry>
<abbrev>RFC2181</abbrev>
<author>
<surname>Elz</surname>
<firstname>R., R. Bush</firstname>
</author>
<title>Clarifications to the <acronym>DNS</acronym>
Specification</title>
<pubdate>July 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2308</abbrev>
<author>
<surname>Andrews</surname>
<firstname>M.</firstname>
</author>
<title>Negative Caching of <acronym>DNS</acronym>
Queries</title>
<pubdate>March 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1995</abbrev>
<author>
<surname>Ohta</surname>
<firstname>M.</firstname>
</author>
<title>Incremental Zone Transfer in <acronym>DNS</acronym></title>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1996</abbrev>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<title>A Mechanism for Prompt Notification of Zone Changes</title>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2136</abbrev>
<authorgroup>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<author>
<firstname>S.</firstname>
<surname>Thomson</surname>
</author>
<author>
<firstname>Y.</firstname>
<surname>Rekhter</surname>
</author>
<author>
<firstname>J.</firstname>
<surname>Bound</surname>
</author>
</authorgroup>
<title>Dynamic Updates in the Domain Name System</title>
<pubdate>April 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2671</abbrev>
<authorgroup>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>Extension Mechanisms for DNS (EDNS0)</title>
<pubdate>August 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2672</abbrev>
<authorgroup>
<author>
<firstname>M.</firstname>
<surname>Crawford</surname>
</author>
</authorgroup>
<title>Non-Terminal DNS Name Redirection</title>
<pubdate>August 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2845</abbrev>
<authorgroup>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<author>
<firstname>O.</firstname>
<surname>Gudmundsson</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
</author>
<author>
<firstname>B.</firstname>
<surname>Wellington</surname>
</author>
</authorgroup>
<title>Secret Key Transaction Authentication for <acronym>DNS</acronym> (TSIG)</title>
<pubdate>May 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2930</abbrev>
<authorgroup>
<author>
<firstname>D.</firstname>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
</author>
</authorgroup>
<title>Secret Key Establishment for DNS (TKEY RR)</title>
<pubdate>September 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2931</abbrev>
<authorgroup>
<author>
<firstname>D.</firstname>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
</author>
</authorgroup>
<title>DNS Request and Transaction Signatures (SIG(0)s)</title>
<pubdate>September 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3007</abbrev>
<authorgroup>
<author>
<firstname>B.</firstname>
<surname>Wellington</surname>
</author>
</authorgroup>
<title>Secure Domain Name System (DNS) Dynamic Update</title>
<pubdate>November 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3645</abbrev>
<authorgroup>
<author>
<firstname>S.</firstname>
<surname>Kwan</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Garg</surname>
</author>
<author>
<firstname>J.</firstname>
<surname>Gilroy</surname>
</author>
<author>
<firstname>L.</firstname>
<surname>Esibov</surname>
</author>
<author>
<firstname>J.</firstname>
<surname>Westhead</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Hall</surname>
</author>
</authorgroup>
<title>Generic Security Service Algorithm for Secret
Key Transaction Authentication for DNS
(GSS-TSIG)</title>
<pubdate>October 2003</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title><acronym>DNS</acronym> Security Proposed Standards</title>
<biblioentry>
<abbrev>RFC3225</abbrev>
<authorgroup>
<author>
<firstname>D.</firstname>
<surname>Conrad</surname>
</author>
</authorgroup>
<title>Indicating Resolver Support of DNSSEC</title>
<pubdate>December 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3833</abbrev>
<authorgroup>
<author>
<firstname>D.</firstname>
<surname>Atkins</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Austein</surname>
</author>
</authorgroup>
<title>Threat Analysis of the Domain Name System (DNS)</title>
<pubdate>August 2004</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4033</abbrev>
<authorgroup>
<author>
<firstname>R.</firstname>
<surname>Arends</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Austein</surname>
</author>
<author>
<firstname>M.</firstname>
<surname>Larson</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Massey</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Rose</surname>
</author>
</authorgroup>
<title>DNS Security Introduction and Requirements</title>
<pubdate>March 2005</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4034</abbrev>
<authorgroup>
<author>
<firstname>R.</firstname>
<surname>Arends</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Austein</surname>
</author>
<author>
<firstname>M.</firstname>
<surname>Larson</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Massey</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Rose</surname>
</author>
</authorgroup>
<title>Resource Records for the DNS Security Extensions</title>
<pubdate>March 2005</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4035</abbrev>
<authorgroup>
<author>
<firstname>R.</firstname>
<surname>Arends</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Austein</surname>
</author>
<author>
<firstname>M.</firstname>
<surname>Larson</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Massey</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Rose</surname>
</author>
</authorgroup>
<title>Protocol Modifications for the DNS
Security Extensions</title>
<pubdate>March 2005</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Other Important RFCs About <acronym>DNS</acronym>
Implementation</title>
<biblioentry>
<abbrev>RFC1535</abbrev>
<author>
<surname>Gavron</surname>
<firstname>E.</firstname>
</author>
<title>A Security Problem and Proposed Correction With Widely
Deployed <acronym>DNS</acronym> Software.</title>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1536</abbrev>
<authorgroup>
<author>
<surname>Kumar</surname>
<firstname>A.</firstname>
</author>
<author>
<firstname>J.</firstname>
<surname>Postel</surname>
</author>
<author>
<firstname>C.</firstname>
<surname>Neuman</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Danzig</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Miller</surname>
</author>
</authorgroup>
<title>Common <acronym>DNS</acronym> Implementation
Errors and Suggested Fixes</title>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1982</abbrev>
<authorgroup>
<author>
<surname>Elz</surname>
<firstname>R.</firstname>
</author>
<author>
<firstname>R.</firstname>
<surname>Bush</surname>
</author>
</authorgroup>
<title>Serial Number Arithmetic</title>
<pubdate>August 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC4074</abbrev>
<authorgroup>
<author>
<surname>Morishita</surname>
<firstname>Y.</firstname>
</author>
<author>
<firstname>T.</firstname>
<surname>Jinmei</surname>
</author>
</authorgroup>
<title>Common Misbehaviour Against <acronym>DNS</acronym>
Queries for IPv6 Addresses</title>
<pubdate>May 2005</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Resource Record Types</title>
<biblioentry>
<abbrev>RFC1183</abbrev>
<authorgroup>
<author>
<surname>Everhart</surname>
<firstname>C.F.</firstname>
</author>
<author>
<firstname>L. A.</firstname>
<surname>Mamakos</surname>
</author>
<author>
<firstname>R.</firstname>
<surname>Ullmann</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Mockapetris</surname>
</author>
</authorgroup>
<title>New <acronym>DNS</acronym> RR Definitions</title>
<pubdate>October 1990</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1706</abbrev>
<authorgroup>
<author>
<surname>Manning</surname>
<firstname>B.</firstname>
</author>
<author>
<firstname>R.</firstname>
<surname>Colella</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> NSAP Resource Records</title>
<pubdate>October 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2168</abbrev>
<authorgroup>
<author>
<surname>Daniel</surname>
<firstname>R.</firstname>
</author>
<author>
<firstname>M.</firstname>
<surname>Mealling</surname>
</author>
</authorgroup>
<title>Resolution of Uniform Resource Identifiers using
the Domain Name System</title>
<pubdate>June 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1876</abbrev>
<authorgroup>
<author>
<surname>Davis</surname>
<firstname>C.</firstname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
<author>
<firstname>T.</firstname>
<firstname>Goodwin</firstname>
</author>
<author>
<firstname>I.</firstname>
<surname>Dickinson</surname>
</author>
</authorgroup>
<title>A Means for Expressing Location Information in the
Domain
Name System</title>
<pubdate>January 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2052</abbrev>
<authorgroup>
<author>
<surname>Gulbrandsen</surname>
<firstname>A.</firstname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>A <acronym>DNS</acronym> RR for Specifying the
Location of
Services.</title>
<pubdate>October 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2163</abbrev>
<author>
<surname>Allocchio</surname>
<firstname>A.</firstname>
</author>
<title>Using the Internet <acronym>DNS</acronym> to
Distribute MIXER
Conformant Global Address Mapping</title>
<pubdate>January 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2230</abbrev>
<author>
<surname>Atkinson</surname>
<firstname>R.</firstname>
</author>
<title>Key Exchange Delegation Record for the <acronym>DNS</acronym></title>
<pubdate>October 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2536</abbrev>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
<title>DSA KEYs and SIGs in the Domain Name System (DNS)</title>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2537</abbrev>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
<title>RSA/MD5 KEYs and SIGs in the Domain Name System (DNS)</title>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2538</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
<author>
<surname>Gudmundsson</surname>
<firstname>O.</firstname>
</author>
</authorgroup>
<title>Storing Certificates in the Domain Name System (DNS)</title>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2539</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
</authorgroup>
<title>Storage of Diffie-Hellman Keys in the Domain Name System (DNS)</title>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2540</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
</authorgroup>
<title>Detached Domain Name System (DNS) Information</title>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2782</abbrev>
<author>
<surname>Gulbrandsen</surname>
<firstname>A.</firstname>
</author>
<author>
<surname>Vixie</surname>
<firstname>P.</firstname>
</author>
<author>
<surname>Esibov</surname>
<firstname>L.</firstname>
</author>
<title>A DNS RR for specifying the location of services (DNS SRV)</title>
<pubdate>February 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2915</abbrev>
<author>
<surname>Mealling</surname>
<firstname>M.</firstname>
</author>
<author>
<surname>Daniel</surname>
<firstname>R.</firstname>
</author>
<title>The Naming Authority Pointer (NAPTR) DNS Resource Record</title>
<pubdate>September 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3110</abbrev>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
<title>RSA/SHA-1 SIGs and RSA KEYs in the Domain Name System (DNS)</title>
<pubdate>May 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3123</abbrev>
<author>
<surname>Koch</surname>
<firstname>P.</firstname>
</author>
<title>A DNS RR Type for Lists of Address Prefixes (APL RR)</title>
<pubdate>June 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3596</abbrev>
<authorgroup>
<author>
<surname>Thomson</surname>
<firstname>S.</firstname>
</author>
<author>
<firstname>C.</firstname>
<surname>Huitema</surname>
</author>
<author>
<firstname>V.</firstname>
<surname>Ksinant</surname>
</author>
<author>
<firstname>M.</firstname>
<surname>Souissi</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> Extensions to support IP
version 6</title>
<pubdate>October 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3597</abbrev>
<author>
<surname>Gustafsson</surname>
<firstname>A.</firstname>
</author>
<title>Handling of Unknown DNS Resource Record (RR) Types</title>
<pubdate>September 2003</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title><acronym>DNS</acronym> and the Internet</title>
<biblioentry>
<abbrev>RFC1101</abbrev>
<author>
<surname>Mockapetris</surname>
<firstname>P. V.</firstname>
</author>
<title><acronym>DNS</acronym> Encoding of Network Names
and Other Types</title>
<pubdate>April 1989</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1123</abbrev>
<author>
<surname>Braden</surname>
<surname>R.</surname>
</author>
<title>Requirements for Internet Hosts - Application and
Support</title>
<pubdate>October 1989</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1591</abbrev>
<author>
<surname>Postel</surname>
<firstname>J.</firstname>
</author>
<title>Domain Name System Structure and Delegation</title>
<pubdate>March 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2317</abbrev>
<authorgroup>
<author>
<surname>Eidnes</surname>
<firstname>H.</firstname>
</author>
<author>
<firstname>G.</firstname>
<surname>de Groot</surname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>Classless IN-ADDR.ARPA Delegation</title>
<pubdate>March 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2826</abbrev>
<authorgroup>
<author>
<surname>Internet Architecture Board</surname>
</author>
</authorgroup>
<title>IAB Technical Comment on the Unique DNS Root</title>
<pubdate>May 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2929</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<firstname>D.</firstname>
<lineage>3rd</lineage>
</author>
<author>
<surname>Brunner-Williams</surname>
<firstname>E.</firstname>
</author>
<author>
<surname>Manning</surname>
<firstname>B.</firstname>
</author>
</authorgroup>
<title>Domain Name System (DNS) IANA Considerations</title>
<pubdate>September 2000</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title><acronym>DNS</acronym> Operations</title>
<biblioentry>
<abbrev>RFC1033</abbrev>
<author>
<surname>Lottor</surname>
<firstname>M.</firstname>
</author>
<title>Domain administrators operations guide.</title>
<pubdate>November 1987</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1537</abbrev>
<author>
<surname>Beertema</surname>
<firstname>P.</firstname>
</author>
<title>Common <acronym>DNS</acronym> Data File
Configuration Errors</title>
<pubdate>October 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1912</abbrev>
<author>
<surname>Barr</surname>
<firstname>D.</firstname>
</author>
<title>Common <acronym>DNS</acronym> Operational and
Configuration Errors</title>
<pubdate>February 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2010</abbrev>
<authorgroup>
<author>
<surname>Manning</surname>
<firstname>B.</firstname>
</author>
<author>
<firstname>P.</firstname>
<surname>Vixie</surname>
</author>
</authorgroup>
<title>Operational Criteria for Root Name Servers.</title>
<pubdate>October 1996</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2219</abbrev>
<authorgroup>
<author>
<surname>Hamilton</surname>
<firstname>M.</firstname>
</author>
<author>
<firstname>R.</firstname>
<surname>Wright</surname>
</author>
</authorgroup>
<title>Use of <acronym>DNS</acronym> Aliases for
Network Services.</title>
<pubdate>October 1997</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Internationalized Domain Names</title>
<biblioentry>
<abbrev>RFC2825</abbrev>
<authorgroup>
<author>
<surname>IAB</surname>
</author>
<author>
<surname>Daigle</surname>
<firstname>R.</firstname>
</author>
</authorgroup>
<title>A Tangled Web: Issues of I18N, Domain Names,
and the Other Internet protocols</title>
<pubdate>May 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3490</abbrev>
<authorgroup>
<author>
<surname>Faltstrom</surname>
<firstname>P.</firstname>
</author>
<author>
<surname>Hoffman</surname>
<firstname>P.</firstname>
</author>
<author>
<surname>Costello</surname>
<firstname>A.</firstname>
</author>
</authorgroup>
<title>Internationalizing Domain Names in Applications (IDNA)</title>
<pubdate>March 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3491</abbrev>
<authorgroup>
<author>
<surname>Hoffman</surname>
<firstname>P.</firstname>
</author>
<author>
<surname>Blanchet</surname>
<firstname>M.</firstname>
</author>
</authorgroup>
<title>Nameprep: A Stringprep Profile for Internationalized Domain Names</title>
<pubdate>March 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3492</abbrev>
<authorgroup>
<author>
<surname>Costello</surname>
<firstname>A.</firstname>
</author>
</authorgroup>
<title>Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in
Applications (IDNA)</title>
<pubdate>March 2003</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Other <acronym>DNS</acronym>-related RFCs</title>
<note>
<para>
Note: the following list of RFCs, although
<acronym>DNS</acronym>-related, are not
concerned with implementing software.
</para>
</note>
<biblioentry>
<abbrev>RFC1464</abbrev>
<author>
<surname>Rosenbaum</surname>
<firstname>R.</firstname>
</author>
<title>Using the Domain Name System To Store Arbitrary String
Attributes</title>
<pubdate>May 1993</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1713</abbrev>
<author>
<surname>Romao</surname>
<firstname>A.</firstname>
</author>
<title>Tools for <acronym>DNS</acronym> Debugging</title>
<pubdate>November 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC1794</abbrev>
<author>
<surname>Brisco</surname>
<firstname>T.</firstname>
</author>
<title><acronym>DNS</acronym> Support for Load
Balancing</title>
<pubdate>April 1995</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2240</abbrev>
<author>
<surname>Vaughan</surname>
<firstname>O.</firstname>
</author>
<title>A Legal Basis for Domain Name Allocation</title>
<pubdate>November 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2345</abbrev>
<authorgroup>
<author>
<surname>Klensin</surname>
<firstname>J.</firstname>
</author>
<author>
<firstname>T.</firstname>
<surname>Wolf</surname>
</author>
<author>
<firstname>G.</firstname>
<surname>Oglesby</surname>
</author>
</authorgroup>
<title>Domain Names and Company Name Retrieval</title>
<pubdate>May 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2352</abbrev>
<author>
<surname>Vaughan</surname>
<firstname>O.</firstname>
</author>
<title>A Convention For Using Legal Names as Domain Names</title>
<pubdate>May 1998</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3071</abbrev>
<authorgroup>
<author>
<surname>Klensin</surname>
<firstname>J.</firstname>
</author>
</authorgroup>
<title>Reflections on the DNS, RFC 1591, and Categories of Domains</title>
<pubdate>February 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3258</abbrev>
<authorgroup>
<author>
<surname>Hardie</surname>
<firstname>T.</firstname>
</author>
</authorgroup>
<title>Distributing Authoritative Name Servers via
Shared Unicast Addresses</title>
<pubdate>April 2002</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3901</abbrev>
<authorgroup>
<author>
<surname>Durand</surname>
<firstname>A.</firstname>
</author>
<author>
<firstname>J.</firstname>
<surname>Ihren</surname>
</author>
</authorgroup>
<title>DNS IPv6 Transport Operational Guidelines</title>
<pubdate>September 2004</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Obsolete and Unimplemented Experimental RFC</title>
<biblioentry>
<abbrev>RFC1712</abbrev>
<authorgroup>
<author>
<surname>Farrell</surname>
<firstname>C.</firstname>
</author>
<author>
<firstname>M.</firstname>
<surname>Schulze</surname>
</author>
<author>
<firstname>S.</firstname>
<surname>Pleitner</surname>
</author>
<author>
<firstname>D.</firstname>
<surname>Baldoni</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> Encoding of Geographical
Location</title>
<pubdate>November 1994</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2673</abbrev>
<authorgroup>
<author>
<surname>Crawford</surname>
<firstname>M.</firstname>
</author>
</authorgroup>
<title>Binary Labels in the Domain Name System</title>
<pubdate>August 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2874</abbrev>
<authorgroup>
<author>
<surname>Crawford</surname>
<firstname>M.</firstname>
</author>
<author>
<surname>Huitema</surname>
<firstname>C.</firstname>
</author>
</authorgroup>
<title>DNS Extensions to Support IPv6 Address Aggregation
and Renumbering</title>
<pubdate>July 2000</pubdate>
</biblioentry>
</bibliodiv>
<bibliodiv>
<title>Obsoleted DNS Security RFCs</title>
<note>
<para>
Most of these have been consolidated into RFC4033,
RFC4034 and RFC4035 which collectively describe DNSSECbis.
</para>
</note>
<biblioentry>
<abbrev>RFC2065</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
<firstname>D.</firstname>
</author>
<author>
<firstname>C.</firstname>
<surname>Kaufman</surname>
</author>
</authorgroup>
<title>Domain Name System Security Extensions</title>
<pubdate>January 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2137</abbrev>
<author>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
<firstname>D.</firstname>
</author>
<title>Secure Domain Name System Dynamic Update</title>
<pubdate>April 1997</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC2535</abbrev>
<authorgroup>
<author>
<surname>Eastlake</surname>
<lineage>3rd</lineage>
<firstname>D.</firstname>
</author>
</authorgroup>
<title>Domain Name System Security Extensions</title>
<pubdate>March 1999</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3008</abbrev>
<authorgroup>
<author>
<surname>Wellington</surname>
<firstname>B.</firstname>
</author>
</authorgroup>
<title>Domain Name System Security (DNSSEC)
Signing Authority</title>
<pubdate>November 2000</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3090</abbrev>
<authorgroup>
<author>
<surname>Lewis</surname>
<firstname>E.</firstname>
</author>
</authorgroup>
<title>DNS Security Extension Clarification on Zone Status</title>
<pubdate>March 2001</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3445</abbrev>
<authorgroup>
<author>
<surname>Massey</surname>
<firstname>D.</firstname>
</author>
<author>
<surname>Rose</surname>
<firstname>S.</firstname>
</author>
</authorgroup>
<title>Limiting the Scope of the KEY Resource Record (RR)</title>
<pubdate>December 2002</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3655</abbrev>
<authorgroup>
<author>
<surname>Wellington</surname>
<firstname>B.</firstname>
</author>
<author>
<surname>Gudmundsson</surname>
<firstname>O.</firstname>
</author>
</authorgroup>
<title>Redefinition of DNS Authenticated Data (AD) bit</title>
<pubdate>November 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3658</abbrev>
<authorgroup>
<author>
<surname>Gudmundsson</surname>
<firstname>O.</firstname>
</author>
</authorgroup>
<title>Delegation Signer (DS) Resource Record (RR)</title>
<pubdate>December 2003</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3755</abbrev>
<authorgroup>
<author>
<surname>Weiler</surname>
<firstname>S.</firstname>
</author>
</authorgroup>
<title>Legacy Resolver Compatibility for Delegation Signer (DS)</title>
<pubdate>May 2004</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3757</abbrev>
<authorgroup>
<author>
<surname>Kolkman</surname>
<firstname>O.</firstname>
</author>
<author>
<surname>Schlyter</surname>
<firstname>J.</firstname>
</author>
<author>
<surname>Lewis</surname>
<firstname>E.</firstname>
</author>
</authorgroup>
<title>Domain Name System KEY (DNSKEY) Resource Record
(RR) Secure Entry Point (SEP) Flag</title>
<pubdate>April 2004</pubdate>
</biblioentry>
<biblioentry>
<abbrev>RFC3845</abbrev>
<authorgroup>
<author>
<surname>Schlyter</surname>
<firstname>J.</firstname>
</author>
</authorgroup>
<title>DNS Security (DNSSEC) NextSECure (NSEC) RDATA Format</title>
<pubdate>August 2004</pubdate>
</biblioentry>
</bibliodiv>
</bibliography>
</sect2>
<sect2 id="internet_drafts">
<title>Internet Drafts</title>
<para>
Internet Drafts (IDs) are rough-draft working documents of
the Internet Engineering Task Force. They are, in essence, RFCs
in the preliminary stages of development. Implementors are
cautioned not
to regard IDs as archival, and they should not be quoted or cited
in any formal documents unless accompanied by the disclaimer that
they are "works in progress." IDs have a lifespan of six months
after which they are deleted unless updated by their authors.
</para>
</sect2>
<sect2>
<title>Other Documents About <acronym>BIND</acronym></title>
<para/>
<bibliography>
<biblioentry>
<authorgroup>
<author>
<surname>Albitz</surname>
<firstname>Paul</firstname>
</author>
<author>
<firstname>Cricket</firstname>
<surname>Liu</surname>
</author>
</authorgroup>
<title><acronym>DNS</acronym> and <acronym>BIND</acronym></title>
<copyright>
<year>1998</year>
<holder>Sebastopol, CA: O'Reilly and Associates</holder>
</copyright>
</biblioentry>
</bibliography>
</sect2>
</sect1>
<xi:include href="libdns.xml"/>
</appendix>
<reference id="Bv9ARM.ch10">
<title>Manual pages</title>
<xi:include href="../../bin/dig/dig.docbook"/>
<xi:include href="../../bin/dig/host.docbook"/>
<xi:include href="../../bin/dnssec/dnssec-dsfromkey.docbook"/>
<xi:include href="../../bin/dnssec/dnssec-keyfromlabel.docbook"/>
<xi:include href="../../bin/dnssec/dnssec-keygen.docbook"/>
<xi:include href="../../bin/dnssec/dnssec-revoke.docbook"/>
<xi:include href="../../bin/dnssec/dnssec-settime.docbook"/>
<xi:include href="../../bin/dnssec/dnssec-signzone.docbook"/>
<xi:include href="../../bin/check/named-checkconf.docbook"/>
<xi:include href="../../bin/check/named-checkzone.docbook"/>
<xi:include href="../../bin/named/named.docbook"/>
<xi:include href="../../bin/tools/named-journalprint.docbook"/>
<!-- named.conf.docbook and others? -->
<xi:include href="../../bin/nsupdate/nsupdate.docbook"/>
<xi:include href="../../bin/rndc/rndc.docbook"/>
<xi:include href="../../bin/rndc/rndc.conf.docbook"/>
<xi:include href="../../bin/confgen/rndc-confgen.docbook"/>
<xi:include href="../../bin/confgen/ddns-confgen.docbook"/>
<xi:include href="../../bin/tools/arpaname.docbook"/>
<xi:include href="../../bin/tools/genrandom.docbook"/>
<xi:include href="../../bin/tools/isc-hmac-fixup.docbook"/>
<xi:include href="../../bin/tools/nsec3hash.docbook"/>
</reference>
</book>
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