#!/usr/bin/perl -w
use strict;
use Net::DNS;

sub usage {
    print STDERR "Usage: $0 ip-address\n";
    exit(1);
}

usage() unless (@ARGV == 1);

# generic resolver
my $res0 = new Net::DNS::Resolver;

my $ipv4 = $ARGV[0];

my $rev_domain = join(".", reverse (split(/\./, $ipv4)), "in-addr", "arpa");
print STDERR "$rev_domain\n";

my $reply = $res0->send($rev_domain, 'PTR');

if ($reply->answer) {
    for my $rr ($reply->answer) {
        if ($rr->type eq 'PTR') {
            print STDERR "\t", $rr->ptrdname, "\n";
            check_a($rr->ptrdname, $ipv4);
        }
    }
} elsif ($reply->authority) {
    for my $rr ($reply->authority) {
        if ($rr->type eq 'SOA') {
            print STDERR "\t", $rr->mname, "\n";
            my $res1 = Net::DNS::Resolver->new();
            $res1->nameservers($rr->mname);
            my @zone = $res1->axfr($rev_domain);
            for my $rr (@zone) {
                if ($rr->type eq 'PTR') {
                    print STDERR "\t\t", $rr->ptrdname, "\n";
                    my $ipv4 = join(".", (reverse(split(/\./, $rr->name)))[2..5]);
                    check_a($rr->ptrdname, $ipv4);
                }
            }
        }
    }
} else {
    $reply->print
}

sub check_a {
    my ($domain_name, $a) = @_;
    # check that $domain_name resolves to $a

    my $reply = $res0->send($domain_name, 'A');

    if ($reply->answer) {
        for my $rr ($reply->answer) {
            if ($rr->type eq 'A') {
                print STDERR "\t\t", $rr->address, "\n";
                if ($rr->address eq $a) {
                    print STDERR "\t\t\tfound\n";
                    return 1;
                }
            }
        }
    }
    print " $a $domain_name FWD_FAIL\n";
    return 0;
}