I know there are a plethora of $_SERVER variables headers available for IP address retrieval. I was wondering if there is a general consensus as to how to most accurately retrieve a user’s real IP address (well knowing no method is perfect) using said variables?
I spent some time trying to find an in depth solution and came up with the following code based on a number of sources. I would love it if somebody could please poke holes in the answer or shed some light on something perhaps more accurate.
edit includes optimizations from @Alix
/**
* Retrieves the best guess of the client's actual IP address.
* Takes into account numerous HTTP proxy headers due to variations
* in how different ISPs handle IP addresses in headers between hops.
*/
public function get_ip_address() {
// Check for shared internet/ISP IP
if (!empty($_SERVER['HTTP_CLIENT_IP']) && $this->validate_ip($_SERVER['HTTP_CLIENT_IP']))
return $_SERVER['HTTP_CLIENT_IP'];
// Check for IPs passing through proxies
if (!empty($_SERVER['HTTP_X_FORWARDED_FOR'])) {
// Check if multiple IP addresses exist in var
$iplist = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
foreach ($iplist as $ip) {
if ($this->validate_ip($ip))
return $ip;
}
}
}
if (!empty($_SERVER['HTTP_X_FORWARDED']) && $this->validate_ip($_SERVER['HTTP_X_FORWARDED']))
return $_SERVER['HTTP_X_FORWARDED'];
if (!empty($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']) && $this->validate_ip($_SERVER['HTTP_X_CLUSTER_CLIENT_IP']))
return $_SERVER['HTTP_X_CLUSTER_CLIENT_IP'];
if (!empty($_SERVER['HTTP_FORWARDED_FOR']) && $this->validate_ip($_SERVER['HTTP_FORWARDED_FOR']))
return $_SERVER['HTTP_FORWARDED_FOR'];
if (!empty($_SERVER['HTTP_FORWARDED']) && $this->validate_ip($_SERVER['HTTP_FORWARDED']))
return $_SERVER['HTTP_FORWARDED'];
// Return unreliable IP address since all else failed
return $_SERVER['REMOTE_ADDR'];
}
/**
* Ensures an IP address is both a valid IP address and does not fall within
* a private network range.
*
* @access public
* @param string $ip
*/
public function validate_ip($ip) {
if (filter_var($ip, FILTER_VALIDATE_IP,
FILTER_FLAG_IPV4 |
FILTER_FLAG_IPV6 |
FILTER_FLAG_NO_PRIV_RANGE |
FILTER_FLAG_NO_RES_RANGE) === false)
return false;
self::$ip = $ip;
return true;
}
Words of Warning (update)
REMOTE_ADDR still represents the most reliable source of an IP address. The other $_SERVER variables mentioned here can be spoofed by a remote client very easily. The purpose of this solution is to attempt to determine the IP address of a client sitting behind a proxy. For your general purposes, you might consider using this in combination with the IP address returned directly from $_SERVER['REMOTE_ADDR'] and storing both.
For 99.9% of users this solution will suit your needs perfectly. It will not protect you from the 0.1% of malicious users looking to abuse your system by injecting their own request headers. If relying on IP addresses for something mission critical, resort to REMOTE_ADDR and don’t bother catering to those behind a proxy.
