Edit File: README.NIS
@(#) 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