Web에서 Proxy를 쓰는 사용자 Real IP 구하기

<?php 
 function getRealIpAddr(){ 
    if(!empty($_SERVER['HTTP_CLIENT_IP']) && getenv('HTTP_CLIENT_IP')){ 
        return $_SERVER['HTTP_CLIENT_IP']; 
    }
    elseif(!empty($_SERVER['HTTP_X_FORWARDED_FOR']) && getenv('HTTP_X_FORWARDED_FOR')){ 
        return $_SERVER['HTTP_X_FORWARDED_FOR']; 
    }
    elseif(!empty($_SERVER['REMOTE_HOST']) && getenv('REMOTE_HOST')){ 
        return $_SERVER['REMOTE_HOST']; 
    }
    elseif(!empty($_SERVER['REMOTE_ADDR']) && getenv('REMOTE_ADDR')){ 
        return $_SERVER['REMOTE_ADDR']; 
    } 
    return false; 
 }


 if($ip = getRealIpAddr()){
     echo $ip;
 }
 ?>