CloudFlare and logging visitor IP addresses via in PHP

Update: CloudFlare has released a module mod_cloudflare for apache, the module will log and display the actual visitor IP Addresses rather than those accessed by cloudflare! https://www.cloudflare.com/resources-downloads#mod_cloudflare (Answer by: olimortimer)

If you dont have access to the apache runtime you can use the script below, this will allow you to check if the connection was through cloudflare and get the users ip.

I am rewriting my answer i used for another question "CloudFlare DNS / direct IP identifier"

Cloudflare's ips are stored in public so you can go view them here then check if the ip is from cloudflare (this will allow us to get the real ip from the http header HTTP_CF_CONNECTING_IP).

If you are using this to disable all non cf connections or vice versa, i recommend you to have a single php script file that gets called before every other script such as a common.php or pagestart.php etc.

function ip_in_range($ip, $range) {
    if (strpos($range, '/') == false)
        $range .= '/32';

    // $range is in IP/CIDR format eg 127.0.0.1/24
    list($range, $netmask) = explode('/', $range, 2);
    $range_decimal = ip2long($range);
    $ip_decimal = ip2long($ip);
    $wildcard_decimal = pow(2, (32 - $netmask)) - 1;
    $netmask_decimal = ~ $wildcard_decimal;
    return (($ip_decimal & $netmask_decimal) == ($range_decimal & $netmask_decimal));
}

function _cloudflare_CheckIP($ip) {
    $cf_ips = array(
        '199.27.128.0/21',
        '173.245.48.0/20',
        '103.21.244.0/22',
        '103.22.200.0/22',
        '103.31.4.0/22',
        '141.101.64.0/18',
        '108.162.192.0/18',
        '190.93.240.0/20',
        '188.114.96.0/20',
        '197.234.240.0/22',
        '198.41.128.0/17',
        '162.158.0.0/15',
        '104.16.0.0/12',
    );
    $is_cf_ip = false;
    foreach ($cf_ips as $cf_ip) {
        if (ip_in_range($ip, $cf_ip)) {
            $is_cf_ip = true;
            break;
        }
    } return $is_cf_ip;
}

function _cloudflare_Requests_Check() {
    $flag = true;

    if(!isset($_SERVER['HTTP_CF_CONNECTING_IP']))   $flag = false;
    if(!isset($_SERVER['HTTP_CF_IPCOUNTRY']))       $flag = false;
    if(!isset($_SERVER['HTTP_CF_RAY']))             $flag = false;
    if(!isset($_SERVER['HTTP_CF_VISITOR']))         $flag = false;
    return $flag;
}

function isCloudflare() {
    $ipCheck        = _cloudflare_CheckIP($_SERVER['REMOTE_ADDR']);
    $requestCheck   = _cloudflare_Requests_Check();
    return ($ipCheck && $requestCheck);
}

// Use when handling ip's
function getRequestIP() {
    $check = isCloudflare();

    if($check) {
        return $_SERVER['HTTP_CF_CONNECTING_IP'];
    } else {
        return $_SERVER['REMOTE_ADDR'];
    }
}

To use the script it's quite simple:

$ip = getRequestIP();
$cf = isCloudflare();

if($cf) echo "Connection is through cloudflare: <br>";
else    echo "Connection is not through cloudflare: <br>";

echo "Your actual ip address is: ". $ip;
echo "The server remote address header is: ". $_SERVER['REMOTE_ADDR'];

This script will show you the real ip address and if the request is CF or not!

Extra server variables that are available to cloud flare are:

$_SERVER["HTTP_CF_CONNECTING_IP"] real visitor ip address, this is what you want

$_SERVER["HTTP_CF_IPCOUNTRY"] country of visitor

$_SERVER["HTTP_CF_RAY"]

$_SERVER["HTTP_CF_VISITOR"] this can help you know if its http or https

you can use it like this:

if (isset($_SERVER["HTTP_CF_CONNECTING_IP"])) {
  $_SERVER['REMOTE_ADDR'] = $_SERVER["HTTP_CF_CONNECTING_IP"];
}

If you do this, and the validity of the visiting IP address is important, you might need to verify that the $_SERVER["REMOTE_ADDR"] contains an actual valid cloudflare IP address, because anyone can fake the header if he was able to connect directly to the server IP.