#!/usr/local/bin/perl -w

# $Id: check_soa 264 2005-04-06 09:16:15Z olaf $

=head1 NAME

check_soa - Check a domain's nameservers

=head1 SYNOPSIS

B<check_soa> I<domain>

=head1 DESCRIPTION

B<check_soa> queries each of a domain's nameservers for the Start

of Authority (SOA) record and prints the serial number.  Errors

are printed for nameservers that couldn't be reached or didn't

answer authoritatively.

=head1 AUTHOR

The original Bourne Shell and C versions were printed in

I<DNS and BIND> by Paul Albitz & Cricket Liu.

This Perl version was written by Michael Fuhr <mike@fuhr.org>.

=head1 SEE ALSO

L<perl(1)>, L<axfr>, L<check_zone>, L<mresolv>, L<mx>, L<perldig>, L<Net::DNS>

=cut

use File::Basename;

use Net::DNS;

use strict;

#------------------------------------------------------------------------------

# Get the domain from the command line.

#------------------------------------------------------------------------------

die "Usage: ", basename($0), " domain\n" unless @ARGV == 1;

my ($domain) = @ARGV;

#------------------------------------------------------------------------------

# Find all the nameservers for the domain.

#------------------------------------------------------------------------------

my $res = Net::DNS::Resolver->new();

$res->defnames(0);

$res->retry(2);

my $ns_req = $res->query($domain, "NS");

die "No nameservers found for $domain: ", $res->errorstring, "\n"

	unless defined($ns_req) and ($ns_req->header->ancount > 0);

# Send out non-recursive queries

$res->recurse(0);

# Do not buffer standard out

$| = 1;

#------------------------------------------------------------------------------

# Check the SOA record on each nameserver.

#------------------------------------------------------------------------------

foreach my $nsrr (grep {$_->type eq "NS" } $ns_req->answer) {

	#----------------------------------------------------------------------

	# Set the resolver to query this nameserver.

	#----------------------------------------------------------------------

	my $ns = $nsrr->nsdname;

	# In order to lookup the IP(s) of the nameserver, we need a Resolver

	# object that is set to our local, recursive nameserver.  So we create

	# a new object just to do that.

	my $local_res = Net::DNS::Resolver->new();

	my $a_req = $local_res->query($ns, 'A');

	unless ($a_req) {

		warn "Can not find address for $ns: ", $res->errorstring, "\n";

		next;

	}

	foreach my $ip (map { $_->address } grep { $_->type eq 'A' } $a_req->answer) {

		#----------------------------------------------------------------------

		# Ask this IP.

		#----------------------------------------------------------------------

		$res->nameservers($ip);	

		print "$ns ($ip): ";

		#----------------------------------------------------------------------

		# Get the SOA record.

		#----------------------------------------------------------------------

		my $soa_req = $res->send($domain, 'SOA', 'IN');

		unless (defined($soa_req)) {

			warn $res->errorstring, "\n";

			next;

		}

		#----------------------------------------------------------------------

		# Is this nameserver authoritative for the domain?

		#----------------------------------------------------------------------

		unless ($soa_req->header->aa) {

			warn "isn't authoritative for $domain\n";

			next;

		}

		#----------------------------------------------------------------------

		# We should have received exactly one answer.

		#----------------------------------------------------------------------

		unless ($soa_req->header->ancount == 1) {

			warn "expected 1 answer, got ", $soa_req->header->ancount, "\n";

			next;

		}

		#----------------------------------------------------------------------

		# Did we receive an SOA record?

		#----------------------------------------------------------------------

		unless (($soa_req->answer)[0]->type eq "SOA") {

			warn "expected SOA, got ", ($soa_req->answer)[0]->type, "\n";

			next;

		}

		#----------------------------------------------------------------------

		# Print the serial number.

		#----------------------------------------------------------------------

		print "has serial number ", ($soa_req->answer)[0]->serial, "\n";

	}

}

0;