REGEX: Hostname

<?php
$hostname = '/([a-zA-Z0-9\.\-\_](?:[a-zA-Z0-9\.\-\_]*[a-zA-Z0-9]))/i';
?>

REGEX: IPv4 Address

<?php
$ip = '/(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})/';
?>