Check PTR for every IP in the given block.

check-ptr

#!/usr/bin/perl
# Check PTR for every IP in the given block.

use 5.010;
use strict;
use warnings;
use Readonly;

use Net::Netmask;
use Socket;

Readonly my $BLOCK => '46.4.238.160/28';

my $block = Net::Netmask->new($BLOCK);
for my $ip ($block->enumerate()) {
  my $ptr_name = gethostbyaddr inet_aton($ip), AF_INET;
  my $ptr_ip  = inet_ntoa(scalar gethostbyname $ptr_name);

  if ($ip eq $ptr_ip) {
    say "OK: $ip resolves to $ptr_name";
  } else {
    say "W:  $ip resolves to $ptr_name and it does NOT resolve back, but to $ptr_ip instead.";
  }

}