use Net::DNS;
my $IP = '64.12.116.67';

my($ASN, $network, $network_bits) = @{
    Net::DNS::Resolver->new()
      ->query(join('.', reverse(split(/\./, $IP))).".asn.routeviews.org", "TXT", "IN")
      ->{answer}->[0]->{char_str_list}
};
print "$network/$network_bits\n";