<?php
public function valid_ip($ip, $which = '')
    {
        $which = strtolower($which);

        // First check if filter_var is available
        if (is_callable('filter_var'))
        {
            switch ($which) {
                case 'ipv4':
                    $flag = FILTER_FLAG_IPV4;
                    break;
                case 'ipv6':
                    $flag = FILTER_FLAG_IPV6;
                    break;
                default:
                    $flag = array();
                    break;
            }

            return (bool) filter_var($ip, FILTER_VALIDATE_IP, $flag);
        }

        if ($which !== 'ipv6' && $which !== 'ipv4')
        {
            if (strpos($ip, ':') !== FALSE)
            {
                $which = 'ipv6';
            }
            elseif (strpos($ip, '.') !== FALSE)
            {
                $which = 'ipv4';
            }
            else
            {
                return FALSE;
            }
        }

        $func = '_valid_'.$which;
        return $this->$func($ip);
    }
?>