#!/usr/bin/perl

use Net::DNS

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

for($c = 0; $c <= 255; $c++) {
 for($d = 0; $d <= 255; $d++) {
  $query= $res->query("81.86.$c.$d", "PTR");
  print "81.86.$c.$d" unless $query;
 }
}