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Network Working Group P. Faltstrom
Internet-Draft Cisco
Updates: 3404, 3959 O. Kolkman
(if approved) NLNet
Intended status: Standards Track October 11, 2010
Expires: April 14, 2011
The Uniform Resource Identifier (URI) DNS Resource Record
draft-faltstrom-uri-06.txt
Abstract
This document defines a new DNS resource record, called the Uniform
Resource Identifier (URI) RR, for publishing mappings from hostnames
to URIs.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 14, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability Statement . . . . . . . . . . . . . . . . . . . 3
3. DNS considerations . . . . . . . . . . . . . . . . . . . . . . 4
4. The format of the URI RR . . . . . . . . . . . . . . . . . . . 4
4.1. Ownername, class and type . . . . . . . . . . . . . . . . 4
4.2. Priority . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Weight . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Target . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.5. URI RDATA Wire Format . . . . . . . . . . . . . . . . . . 6
5. Definition of the flag 'D' for NAPTR records . . . . . . . . . 6
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. Homepage at one domain, but two domains in use . . . . . . 7
7. Relation to S-NAPTR . . . . . . . . . . . . . . . . . . . . . 7
8. Relation to U-NAPTR . . . . . . . . . . . . . . . . . . . . . 7
9. Relation to SRV . . . . . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10.1. Registration of the URI Resource Record Type . . . . . . . 8
10.2. Registration of services . . . . . . . . . . . . . . . . . 8
11. Security Considerations . . . . . . . . . . . . . . . . . . . 8
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. RRTYPE Allocation Request . . . . . . . . . . . . . . 9
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
13.1. Normative References . . . . . . . . . . . . . . . . . . . 12
13.2. Non-normative references . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This document explains the use of the Domain Name System (DNS) for
the storage of URIs, and how to resolve hostnames to such URIs that
can be used by various applications. For resolution the application
need to know both the hostname and the protocol that the URI is to be
used for. The protocol is registered by IANA.
Currently, looking up URIs given a hostname uses the DDDS [RFC3401]
application framework with the DNS as a database as specified in RFC
3404 [RFC3404]. This has a number of implications such as the
inability to select what NAPTR records that match the query are
interesting. The RRSet returned will always consist of all URIs
"connected" with the domain in question.
The URI resource record specified in this document enables the
querying party to select which ones of the NAPTR records one is
interested in. This because data in the service field of the NAPTR
record is included in the owner part of the URI resource record type.
Querying for URI resource records is not replacing querying for NAPTR
resource records (or use of S-NAPTR [RFC3958]). Instead, the URI
resource record type provides a complementary mechanism to use when
one already knows what service field is interesting. With it, one
can directly query for the specific subset of the otherwise possibly
large RRSet given back when querying for NAPTR resource records.
This document updates RFC 3958 and RFC 3404 by adding the flag "D" to
the list of defined terminal flags in section 2.2.3 of RFC 3958 and
4.3 of RFC 3404.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[RFC2119].
2. Applicability Statement
In general, it is expected that URI records will be used by clients
for applications where the relevant protocol to be used is known,
but, for example, an extra abstraction is needed in order to separate
a domain name from a point of service (as addressed by the URI). One
example of such a situation is when an organisation has many domain
names, but only one official web page.
Applications MUST know the specific service fields to prepend the
hostname with. Using repetitive queries for URI records MUST NOT be
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a replacement for querying for NAPTR records according to the NAPTR
(DDDS) or S-NAPTR algorithms. NAPTR records serve the purpose to
discover the various services and URIs for looking up access points
for a given service. Those are two very different kinds of needs.
3. DNS considerations
Using prefix labels, such as underscored service tags, prevents the
use of wildcards, as constructs as _s2._s1.*.example.net. are not
possible in the DNS, see RFC 4592 [RFC4592]. Besides, underscored
service tags used for the URI RR (based on the NAPTR service
descriptions) may have slightly different semantics than service tags
used for underscored prefix labels that are used in combination with
other (yet unspecified) RR types. This may cause subtle management
problems when delegation structure that has developed within the
context of URI RRs is also to be used for other RR types. Since the
service labels might be overloaded, applications should carefully
check that the application level protocol is indeed the protocol they
expect.
Subtle management issues may also arise when the delegations from
service to sub service label involves several parties and different
stake holders.
4. The format of the URI RR
This is the presentation format of the URI RR:
Ownername TTL Class URI Priority Weight Target
The URI RR does not cause any kind of Additional Section processing.
4.1. Ownername, class and type
The URI ownername is subject to special conventions.
Just like the SRV RR [RFC2782] the URI RR has service information
encoded in its ownername. In order to encode the service for a
specific owner name one uses service parameters. Valid service
parameters used are those used for SRV resource records, or
registered by IANA for Enumservice Registrations. The Enumservice
Registration parameters are reversed (subtype(s) before type),
prepended with an underscore (_) and prepended to the owner name in
separate labels. The underscore is prepended to the service
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parameters to avoid collisions with DNS labels that occur in nature,
and the order is reversed to make it possible to do delegations, if
needed, to different zones (and therefore providers of DNS).
It should be noted that the usage of a prefix must be described in
detail in for example the Enumservice Registration documentation, or
in a specific document that clarifies potential overload of
parameters in the same URI. Specifically, registered URI schemes are
not automatically acceptable as a service. With the HTTP scheme, one
can for example have multiple methods (GET, PUT, etc), and this with
the same URI.
For example, suppose we are looking for the URI for a service with
Service Parameter "A:B:C" for host example.com.. Then we would query
for (QNAME,QTYPE)=("_C._B._A.example.com","URI")
The type number for the URI record is TBD1 (to be assigned by IANA).
The URI resource record is class independent.
The URI RR has no special TTL requirements.
4.2. Priority
The priority of the target URI in this RR. Its range is 0-65535. A
client MUST attempt to contact the URI with the lowest-numbered
priority it can reach; URIs with the same priority SHOULD be tried in
the order defined by the weight field.
4.3. Weight
A server selection mechanism. The weight field specifies a relative
weight for entries with the same priority. Larger weights SHOULD be
given a proportionately higher probability of being selected. The
range of this number is 0-65535.
4.4. Target
The URI of the target, enclosed in double-quote characters ('"').
Resolution of the URI is according to the definitions for the Scheme
of the URI.
The URI is encoded as one or more <character-string> RFC1035 section
3.3 [RFC1035].
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4.5. URI RDATA Wire Format
The RDATA for a URI RR consists of a 2 octet Priority field, a two
octet Weight field, and a variable length target field.
Priority and Weight are unsigned integers in network byte order.
The Target field contains the URI (without the enclosing double-
quote characters used in the presentation format), encoded as a
sequence of one or more <character-string> (as specified in section
3.3 of RFC 1035 [RFC1035]), where all but the last <character-string>
are filled up to the maximum length of 255 octets.
The Target field can also contain an IRI, but with the additional
requirements that it is in UTF-8 [RFC3629] and possible to convert to
a URI according to section 3.1 of RFC 3987 [RFC3987] and back again
to an IRI according to section 3.2. Other character sets than UTF-8
are not allowed. The domain name part of the IRI can be either an
U-LABEL or A-LABEL as defined in RFC 5890 [RFC5890].
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
/ Target /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5. Definition of the flag 'D' for NAPTR records
This document specifies the flag "D" for use as a flag in NAPTR
records. The flag indicate a terminal NAPTR record because it
denotes the end of the DDDS/NAPTR processing rules. In the case of a
"D" flag, the Replacement field in the NAPTR record, prepended with
the service flags, is used as the Owner of a DNS query for URI
records, and normal URI processing as defined in this document is
applied.
The replacement field MUST NOT include any of the service parameters.
Those are to be prepended (together with underscore) as described in
other places in this document.
The Regexp field in the NAPTR record MUST be empty when the 'D' flag
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is in use.
6. Examples
6.1. Homepage at one domain, but two domains in use
An organisation has the domain names example.com and example.net, but
the official URI http://www.example.com/. Given the service type
"web" and subtype "http" (from the IANA registry), the following URI
Resource Records could be made available in the respective zones
(example.com and example.net):
$ORIGIN example.com.
_http._web IN URI 10 1 "http://www.example.com/"
$ORIGIN example.net.
_http._web IN URI 10 1 "http://www.example.com/"
7. Relation to S-NAPTR
The URI resource record type is not a replacement for the S-NAPTR.
It is instead an extension and the seond step of the S-NAPTR
resolution can resolve a URI resource record instead of using SRV
records and yet another algorithm for how to use SRV records for the
specific protocol.
$ORIGIN example.com.
;; order pref flags
IN NAPTR 100 10 "s" "EM:ProtA" ( ; service
"" ; regexp
_ProtA._tcp.example.com. ; replacement
_ProtA._tcp IN URI "schemeA:service.example.com/example"
8. Relation to U-NAPTR
The URI Resource Record Type, together with S-NAPTR, can be viewed as
a replacement for the U-NAPTR. The URI Resource Record Type is
though only interesting when one know a base domain name, a protocol
and service so that one can compose the record to look up. NAPTR
records of any kind are used to look up what services exists for a
certain domain, which is one step before the URI resource record is
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used.
9. Relation to SRV
The URI Resource Record Type can be viewed as a replacement for the
SRV record. This because it like the SRV record can only be looked
up if one know the base domain, the protocol and the service. It has
a similar functionality, but instead of returning a hostname and port
number, the URI record return a full URI. As such, it can be viewed
as a more powerful resource record than SRV.
10. IANA Considerations
10.1. Registration of the URI Resource Record Type
IANA has assigned Resource Record Type TBD1 for the URI Resource
Record Type and added the line depicted below to the registry named
Resource Record (RR) TYPEs and QTYPEs as defined in BCP 42 RFC 5395
[RFC5395] and located at
http://www.iana.org/assignments/dns-parameters.
TYPE Value and meaning Reference
----------- --------------------------------------------- ---------
URI TBD1 a URI for a service (per the owner name) [RFCXXXX]
10.2. Registration of services
No new registry is needed for the registration of services as the
Enumservice Registrations registry is used also for the URI resource
record type.
11. Security Considerations
The authors do not believe this resource record cause any new
security problems. Deployment must though be done in a proper way as
misconfiguration of this resource record might make it impossible to
reach the service that was originally intended to be accessed.
Using the URI resource record together with security mechanisms that
relies on verification of authentication of hostnames, like TLS,
makes it important to choose the correct domain name when doing the
comparison.
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The basic mechanism works as follows:
1. Announce the fact example.com is hosted at example.org (with
some URL) in DNS
2. Secure the URI resource record with DNSSEC.
3. Verify the TLS (for example) certificate for the connection to
example.org matches, i.e. use the hostname in the URI and not
the hostname used originally when looking up the URI resource
record.
4. If needed, do application layer authentication etc over the then
encrypted connection.
What also can happen is that the URI in the resource record type has
errors in it. Applications using the URI resource record type for
resolution should behave similarly as if the user typed (or copy and
pasted) the URI. At least it must be clear to the user that the
error is not due to any error from his side.
One SHOULD not include userinfo (see User Information, Section 3.2.1,
in RFC 3986 [RFC3986]) in a URI that is used in a URI resource record
as DNS data must be viewed as publicly available information.
12. Acknowledgements
Ideas on how to split the two different kind of queries "What
services exists for this domain name" and "What is the URI for this
service" came from Scott Bradner and Lawrence Conroy. Other people
that have contributed to this document include Richard Barnes, Leslie
Daigle, Olafur Gudmundsson, Ted Hardie, Peter Koch and Penn Pfautz.
Appendix A. RRTYPE Allocation Request
A. Submission Date:
May 23, 2009
B. Submission Type:
[X] New RRTYPE
[ ] Modification to existing RRTYPE
C. Contact Information for submitter:
Name: Patrik Faltstrom
Email Address: paf@cisco.com
International telephone number: +46-8-6859131
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Other contact handles:
(Note: This information will be publicly posted.)
D. Motivation for the new RRTYPE application?
There is no easy way to get from a domain name to a URI (or
IRI). Some mechanisms exists via use of the NAPTR [RFC3403]
resource record. That implies quite complicated rules that are
simplified via the S-NAPTR [RFC3958] specification. But, the
ability to directly look up a URI still exists. This
specification uses a prefix based naming mechanism originated in
the definition of the SRV [RFC2782] resource record, and the
RDATA is a URI, encoded as one text field.
See also above (Section 1).
E. Description of the proposed RR type.
The format of the URI resource record is as follows:
Ownername TTL Class URI Priority Weight Target
The URI RR has service information encoded in its ownername. In
order to encode the service for a specific owner name one uses
service parameters. Valid service parameters used are either
Enumservice Registrations registered by IANA, or prefixes used
for the SRV resource record.
The wire format of the RDATA is as follows:
1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | Weight |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ /
/ Target /
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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F. What existing RRTYPE or RRTYPEs come closest to filling that
need and why are they unsatisfactory?
The RRTYPE that come closest is the NAPTR resource record. It
is for example used in the DDDS and S-NAPTR algorithms. The
main problem with the NAPTR is that selection of what record (or
records) one is interested in is based on data stored in the
RDATA portion of the NAPTR resource record. This, as explained
in RFC 5507 [RFC5507], is not optimal for DNS lookups. Further,
most applications using NAPTR resource records uses regular
expression based rewrite rules for creation of the URI, and that
has shown be complicated to implement.
The second closest RRTYPE is the SRV record that given a
prefixed based naming just like is suggested for the URI
resource record, one get back a port number and domain name.
This can also be used for creation of a URI, but, only URIs
without path components.
G. What mnemonic is requested for the new RRTYPE (optional)?
URI
H. Does the requested RRTYPE make use of any existing IANA Registry
or require the creation of a new IANA sub-registry in DNS
Parameters?
Yes, partially.
One of the mechanisms to select a service is to use the
Enumservice Registry managed by IANA. Another is to use
services and protocols used for SRV records.
I. Does the proposal require/expect any changes in DNS servers/
resolvers that prevent the new type from being processed as an
unknown RRTYPE (see [RFC3597])?
No
J. Comments:
None
13. References
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13.1. Normative References
[E164] ITU-T, "The International Public Telecommunication Number
Plan", Recommendation E.164, May 1997.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3958] Daigle, L. and A. Newton, "Domain-Based Application
Service Location Using SRV RRs and the Dynamic Delegation
Discovery Service (DDDS)", RFC 3958, January 2005.
[RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
Identifiers (IRIs)", RFC 3987, January 2005.
[RFC5395] Eastlake, D., "Domain Name System (DNS) IANA
Considerations", BCP 42, RFC 5395, November 2008.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
13.2. Non-normative references
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3401] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part One: The Comprehensive DDDS", RFC 3401, October 2002.
[RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Three: The Domain Name System (DNS) Database",
RFC 3403, October 2002.
[RFC3404] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Four: The Uniform Resource Identifiers (URI)",
RFC 3404, October 2002.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
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[RFC4592] Lewis, E., "The Role of Wildcards in the Domain Name
System", RFC 4592, July 2006.
[RFC4848] Daigle, L., "Domain-Based Application Service Location
Using URIs and the Dynamic Delegation Discovery Service
(DDDS)", RFC 4848, April 2007.
[RFC5507] IAB, Faltstrom, P., Austein, R., and P. Koch, "Design
Choices When Expanding the DNS", RFC 5507, April 2009.
Authors' Addresses
Patrik Faltstrom
Cisco Systems
Email: paf@cisco.com
Olaf Kolkman
NLnet Labs
Email: olaf@NLnetLabs.nl
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