CloudFlare DNS / direct IP identifier

Question

We started to use cloudflare at my work and I want to understand how the cloudflare knows that I put dns name at my browser and not direct IP.

I mean - how they knows if I put www.mysite.com and NOT 123.34.45.45 as URL on my browser.

Is there any flag at HTTP GET header or any other identifier ?

Many thanks.

Answer 1

There is a way of doing that.

Inside apache instead of doing a public root directory, use VHosts instead they will only respond to a vhost requested. While its better than nothing it still can be displayed through an numerous amount of ways. 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)

I recommend you do it in PHP: 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 "Cloudflare :D<br>";
else    echo "Not cloudflare o_0";

echo "Your actual ip address is: ". $ip;

This script should help you out to check if the request is from CF and not directly though a ip address.

Answer 2

That's how DNS works.

"The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain"