Date: Thu, 22 Jun 2000 20:37:21 -0700 (MST) From: "Chad R. Larson" <chad@DCFinc.com> To: blk@skynet.be (Brad Knowles) Cc: freebsd.stable@lists.craxx.nl, freebsd-stable@FreeBSD.ORG Subject: Re: Weird NSLOOKUP output... Message-ID: <200006230337.UAA07934@freeway.dcfinc.com> In-Reply-To: <v04220815b577cdd16cd8@[195.238.1.121]> from Brad Knowles at "Jun 22, 0 04:10:29 pm"
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As I recall, Brad Knowles wrote:
> It is my understanding that the current version of nslookup is
> unlikely to live much longer. BIND-knowledgeable people I know of
> strongly recommend that you use "dig" instead, and in fact I've
> heard rumours that future versions of nslookup may in fact simply
> be another interface to the "dig" program, or may be a script of
> some sort that simply calls dig.
And, I've become sorta fond of the "host(1)" program, which by
default does pretty much what you would do when looking up a system.
However, as I've noted here before, there is a pitfall. Most
application programs don't call the resolver routines directly.
They call "gethostbyname(3)", which =may= query the /etc/hosts file
before checking with DNS via the resolver. So, if you've overloaded
a DNS address with one in the hosts file (deliberately or
accidentally), your application will not get the same answer you
will get from dig/host/nslookup. Much confusion can result. Don't
ask my how I know this.
Attached is a tiny, no-man-page, trivial utility that wraps a
command line interface around the gethostbyname call specifically to
help sort out such confusions.
-crl
--
Chad R. Larson (CRL15) 602-953-1392 Brother, can you paradigm?
chad@dcfinc.com chad@larsons.org larson1@home.net
DCF, Inc. - 14623 North 49th Place, Scottsdale, Arizona 85254-2207
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Content-Description: command line interface to gethostbyname(3)
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# This is a shell archive. Save it in a file, remove anything before
# this line, and then unpack it by entering "sh file". Note, it may
# create directories; files and directories will be owned by you and
# have default permissions.
#
# This archive contains:
#
# gethost.c
# Makefile
#
echo x - gethost.c
sed 's/^X//' >gethost.c << 'END-of-gethost.c'
X/* $Id: gethost.c,v 1.1 2000/05/17 04:52:06 chad Exp $*/
X
X/*
X * Print the "hostent" information for every host whose name is
X * specified on the command line.
X */
X
X#include <stdio.h>
X#include <sys/types.h>
X#include <netdb.h> /* for struct hostent */
X#include <sys/socket.h> /* for AF_INET */
X#include <netinet/in.h> /* for struct in_addr */
X#include <arpa/inet.h> /* for inet_ntoa() */
X
X#define FALSE 0
X#define TRUE ~FALSE
X
Xmain(argc, argv)
Xint argc;
Xchar **argv;
X{
X register char *ptr;
X register struct hostent *hostptr;
X int tcp_flag = FALSE; /* stream or dgram ? */
X
X if (argc < 2) {
X printf("Usage: %s hostname [...]\n", argv[0]);
X exit(1);
X }
X
X if (argc > 2) { /* use virtual circuit if more than one query */
X tcp_flag = TRUE;
X sethostent(TRUE);
X }
X
X while (--argc > 0) {
X ptr = *++argv;
X if ( (hostptr = gethostbyname(ptr)) == NULL) {
X printf("gethostbyname error for host %s: ", ptr);
X err_ret(h_errno);
X continue;
X }
X printf("\nOfficial host name: %s\n", hostptr->h_name);
X
X /* go through the list of aliases */
X while ( (ptr = *(hostptr->h_aliases)) != NULL) {
X printf(" alias: %s\n", ptr);
X hostptr->h_aliases++;
X }
X
X switch (hostptr->h_addrtype) {
X case AF_INET:
X pr_inet(hostptr->h_addr_list, hostptr->h_length);
X break;
X
X default:
X printf("unknown address type");
X break;
X }
X }
X if (tcp_flag)
X endhostent();
X}
X
X/*
X * Go through a list of Internet addresses,
X * printing each one in dotted-decimal notation.
X */
X
Xpr_inet(listptr, length)
Xchar **listptr;
Xint length;
X{
X struct in_addr *ptr;
X
X while ( (ptr = (struct in_addr *) *listptr++) != NULL)
X printf(" Internet address: %s\n", inet_ntoa(*ptr));
X}
X
X/*
X * Display hostent error code
X */
X
Xerr_ret(err)
Xint err;
X{
X switch (err) {
X case HOST_NOT_FOUND:
X printf("Authoritative Answer Host not found\n");
X break;
X case TRY_AGAIN:
X printf("Non-Authoritive Host not found, or server fail\n");
X break;
X case NO_RECOVERY:
X printf("Non recoverable errors, FORMERR, REFUSED, NOTIMP\n");
X break;
X case NO_DATA:
X printf("Valid name, no data record of requested type\n");
X default:
X printf("Unknown error code %d\n", err);
X break;
X }
X}
END-of-gethost.c
echo x - Makefile
sed 's/^X//' >Makefile << 'END-of-Makefile'
X# Makefile for the host name lookup program
X# $Id: Makefile,v 1.1 2000/05/17 04:52:06 chad Exp $
X
XBINDIR = /usr/local/bin
X
Xgethost: gethost.o
X $(CC) $(CFLAGS) gethost.o -o gethost
X
Xinstall: gethost
X install -C -s gethost $(BINDIR)
X
X.c.o:
X $(CC) $(CFLAGS) -c $<
END-of-Makefile
exit
--ELM961731441-7805-0_--
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