Определение IP пользователя PHP

function ip() {
    if (isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        $ip = $_SERVER['HTTP_X_FORWARDED_FOR'];
    } elseif (isset($_SERVER['HTTP_CLIENT_IP'])) {
        $ip = $_SERVER['HTTP_CLIENT_IP'];
    } else {
        $ip = $_SERVER['REMOTE_ADDR'];
    }
    return $ip;
}