Net_IPv4::ipInNetwork()

<?php

require 'Net/IPv4.php';

$ip   = '10.11.12.13';
$net1 = '10.0.0.1/8';
$net2 = '127.0.0.1/8';

echo Net_IPv4::ipInNetwork($ip, $net1) // bool(true)
echo Net_IPv4::ipInNetwork($ip, $net2) // bool(false)
?>