#!/usr/bin/perl

use strict;
no strict 'refs';
use vars qw($res @foo %name);
use Net::DNS;

$res=new Net::DNS::Resolver;

while (<>)
{
    @foo=split;
    if (!defined($name{$foo[0]}))
    {
        $name{$foo[0]}=&lookup($res, $foo[0]);
    }
    s/^$foo[0]/$name{$foo[0]}/;
    print;
}

sub arpa
{
    my($addr)=@_;
    join(".", reverse(split(/\./, $addr))) . ".in-addr.arpa";
}

sub lookup
{
    my($res, $addr)=@_;
    my $rr;

    my $arpa=&arpa($addr);
QUERY:
    my $query=$res->query($arpa, "PTR");
    if ($query)
    {
        foreach $rr ($query->answer)
        {
            if ($rr->type eq "PTR")
            {
                return $rr->ptrdname;
            }
            elsif ($rr->type eq "CNAME")
            {
#                print STDERR "!!!!!!!!!!!!*******************!!!!!!!!!!!!!!!\n";
#                print STDERR "returned CNAME for $arpa?\n";
#                for (keys(%{$rr}))
#                {
#                    print $_, "=", $rr->{$_}, "\n";
#                }
                $arpa=$rr->cname;
                goto QUERY;
            }
        }
    }
    else
    {
        print STDERR "failed for $addr.\n";
    }
    return $addr;
}