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@(#) README.NIS 1.2 96/02/11 17:24:52
> Problem: I have several [machines] with multiple IP addresses, and
> when they try to connect to a daemon with tcp wrapper, they are often
> rejected. I assume this is due to the -DPARANOID option, and depends
> on which IP address is returned first from the nameserver for a given
> name. This behavior seems to be random, may depend on ordering in
> the YP host map?
[Note: the situation described below no longer exists. Presently, my
internet gateway uses the same IP address on all interfaces. To avoid
confusion I have removed the old name wzv-gw.win.tue.nl from the DNS. I
have kept the discussion below for educational reasons].
NIS was not designed to handle multi-homed hosts. With NIS, each
address should have its own hostname. For example, wzv-gw is my
gateway. It has two interfaces: one connected to the local ethernet,
the other to a serial link. In the NIS it is registered as:
131.155.210.23 wzv-gw-ether
131.155.12.78 wzv-gw-slip
In principle, wzv-gw could be the official name of one of these
interfaces, or it could be an alias for both.
The DNS was designed to handle multi-homed hosts. In the DNS my gateway
is registered in zone win.tue.nl, with one name that has two A records:
wzv-gw IN A 131.155.210.23
IN A 131.155.12.78
And of course there are PTR records in zones 210.155.131.in-addr.arpa
and 12.155.131.in-addr.arpa that point to wzv-gw.win.tue.nl.
This setup does not cause any problems. You can test your name service
with the two programs below. This is what they say on a local NIS client
(both client and server running SunOS 4.1.3_U1):
% gethostbyname wzv-gw
Hostname: wzv-gw.win.tue.nl
Aliases:
Addresses: 131.155.210.23 131.155.12.78
% gethostbyaddr 131.155.210.23
Hostname: wzv-gw-ether
Aliases:
Addresses: 131.155.210.23
% gethostbyaddr 131.155.12.78
Hostname: wzv-gw-slip
Aliases:
Addresses: 131.155.12.78
Things seem less confusing when seen by a NIS client in a different
domain (both client and server running SunOS 4.1.3_U1):
% gethostbyname wzv-gw.win.tue.nl
Hostname: wzv-gw.win.tue.nl
Aliases:
Addresses: 131.155.210.23 131.155.12.78
% gethostbyaddr 131.155.210.23
Hostname: wzv-gw.win.tue.nl
Aliases:
Addresses: 131.155.12.78 131.155.210.23
% gethostbyaddr 131.155.12.78
Hostname: wzv-gw.win.tue.nl
Aliases:
Addresses: 131.155.210.23 131.155.12.78
Alas, Solaris 2.4 still has problems. This is what I get on a Solaris
2.4 NIS client, with a SunOS 4.1.3_U1 NIS server:
% gethostbyname wzv-gw.win.tue.nl
Hostname: wzv-gw.win.tue.nl
Aliases: 131.155.210.23 wzv-gw.win.tue.nl
Addresses: 131.155.12.78
The tcpd source comes with a workaround for this problem. The
workaround is ugly and is not part of the programs attached below.
#! /bin/sh
# This is a shell archive. Remove anything before this line, then unpack
# it by saving it into a file and typing "sh file". To overwrite existing
# files, type "sh file -c". You can also feed this as standard input via
# unshar, or by typing "sh <file", e.g.. If this archive is complete, you
# will see the following message at the end:
# "End of shell archive."
# Contents: gethostbyaddr.c gethostbyname.c
# Wrapped by wietse@wzv on Sun Jan 8 17:08:48 1995
PATH=/bin:/usr/bin:/usr/ucb ; export PATH
if test -f gethostbyaddr.c -a "${1}" != "-c" ; then
echo shar: Will not over-write existing file \"gethostbyaddr.c\"
else
echo shar: Extracting \"gethostbyaddr.c\" \(1073 characters\)
sed "s/^X//" >gethostbyaddr.c <<'END_OF_gethostbyaddr.c'
X /*
X * gethostbyaddr tester. compile with:
X *
X * cc -o gethostbyaddr gethostbyaddr.c (SunOS 4.x)
X *
X * cc -o gethostbyaddr gethostbyaddr.c -lnsl (SunOS 5.x)
X *
X * run as: gethostbyaddr address
X *
X * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
X */
X
X#include <sys/types.h>
X#include <sys/socket.h>
X#include <netinet/in.h>
X#include <arpa/inet.h>
X#include <netdb.h>
X#include <stdio.h>
X
Xmain(argc, argv)
Xint argc;
Xchar **argv;
X{
X struct hostent *hp;
X long addr;
X
X if (argc != 2) {
X fprintf(stderr, "usage: %s i.p.addres\n", argv[0]);
X exit(1);
X }
X addr = inet_addr(argv[1]);
X if (hp = gethostbyaddr((char *) &addr, sizeof(addr), AF_INET)) {
X printf("Hostname:\t%s\n", hp->h_name);
X printf("Aliases:\t");
X while (hp->h_aliases[0])
X printf("%s ", *hp->h_aliases++);
X printf("\n");
X printf("Addresses:\t");
X while (hp->h_addr_list[0])
X printf("%s ", inet_ntoa(*(struct in_addr *) * hp->h_addr_list++));
X printf("\n");
X exit(0);
X }
X fprintf(stderr, "host %s not found\n", argv[1]);
X exit(1);
X}
END_OF_gethostbyaddr.c
if test 1073 -ne `wc -c <gethostbyaddr.c`; then
echo shar: \"gethostbyaddr.c\" unpacked with wrong size!
fi
# end of overwriting check
fi
if test -f gethostbyname.c -a "${1}" != "-c" ; then
echo shar: Will not over-write existing file \"gethostbyname.c\"
else
echo shar: Extracting \"gethostbyname.c\" \(999 characters\)
sed "s/^X//" >gethostbyname.c <<'END_OF_gethostbyname.c'
X /*
X * gethostbyname tester. compile with:
X *
X * cc -o gethostbyname gethostbyname.c (SunOS 4.x)
X *
X * cc -o gethostbyname gethostbyname.c -lnsl (SunOS 5.x)
X *
X * run as: gethostbyname hostname
X *
X * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
X */
X#include <sys/types.h>
X#include <sys/socket.h>
X#include <netinet/in.h>
X#include <arpa/inet.h>
X#include <netdb.h>
X#include <stdio.h>
X
Xmain(argc, argv)
Xint argc;
Xchar **argv;
X{
X struct hostent *hp;
X
X if (argc != 2) {
X fprintf(stderr, "usage: %s hostname\n", argv[0]);
X exit(1);
X }
X if (hp = gethostbyname(argv[1])) {
X printf("Hostname:\t%s\n", hp->h_name);
X printf("Aliases:\t");
X while (hp->h_aliases[0])
X printf("%s ", *hp->h_aliases++);
X printf("\n");
X printf("Addresses:\t");
X while (hp->h_addr_list[0])
X printf("%s ", inet_ntoa(*(struct in_addr *) * hp->h_addr_list++));
X printf("\n");
X exit(0);
X } else {
X fprintf(stderr, "host %s not found\n", argv[1]);
X exit(1);
X }
X}
END_OF_gethostbyname.c
if test 999 -ne `wc -c <gethostbyname.c`; then
echo shar: \"gethostbyname.c\" unpacked with wrong size!
fi
# end of overwriting check
fi
echo shar: End of shell archive.
exit 0
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