Net::DNS can do reverse lookups. This was taken almost verbatim from the docs:

use strict;
use warnings;
use Net::IP;
use Net::DNS;
my $ip = new Net::IP($ARGV[0],4);
print $ip->reverse_ip()."\n";
print "Resolving ...\n";
my $res = Net::DNS::Resolver->new;
my $answer = $res->query($ip->reverse_ip(),'PTR');
my $namer = $answer->{'answer'}[0];
if ($namer->{'ptrdname'}) {
    print "PTR Name: $namer->{'ptrdname'}\n";
} else {
    print "N/A\n";
}
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Gives:

C:\temp>perl revlookup.pl 66.39.54.27
27.54.39.66.in-addr.arpa.
Resolving ...
PTR Name: ads.perlmonks.org
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