PHP: real ip

realip.php

<?php

// Returns the real IP address of the user
function i2c_realip()
{
	// No IP found (will be overwritten by for
	// if any IP is found behind a firewall)
	$ip = FALSE;
	
	// If HTTP_CLIENT_IP is set, then give it priority
	if (!empty($_SERVER["HTTP_CLIENT_IP"])) {
		$ip = $_SERVER["HTTP_CLIENT_IP"];
	}
	
	// User is behind a proxy and check that we discard RFC1918 IP addresses
	// if they are behind a proxy then only figure out which IP belongs to the
	// user.  Might not need any more hackin if there is a squid reverse proxy
	// infront of apache.
	if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {

		// Put the IP's into an array which we shall work with shortly.
		$ips = explode (", ", $_SERVER['HTTP_X_FORWARDED_FOR']);
		if ($ip) { array_unshift($ips, $ip); $ip = FALSE; }

		for ($i = 0; $i < count($ips); $i++) {
			// Skip RFC 1918 IP's 10.0.0.0/8, 172.16.0.0/12 and
			// 192.168.0.0/16
			if (!preg_match('/^(?:10|172\.(?:1[6-9]|2\d|3[01])|192\.168)\./', $ips[$i])) {
				if (version_compare(phpversion(), "5.0.0", ">=")) {
					if (ip2long($ips[$i]) != false) {
						$ip = $ips[$i];
						break;
					}
				} else {
					if (ip2long($ips[$i]) != -1) {
						$ip = $ips[$i];
						break;
					}
				}
			}
		}
	}

	// Return with the found IP or the remote address
	return ($ip ? $ip : $_SERVER['REMOTE_ADDR']);
}