определить IP-адрес пользователя учитывая прокси-сервер

function getip()
{
  if (getenv("HTTP_CLIENT_IP") && strcasecmp(getenv("HTTP_CLIENT_IP"),"unknown"))
    $ip = getenv("HTTP_CLIENT_IP");
 
  elseif (getenv("HTTP_X_FORWARDED_FOR") && strcasecmp(getenv("HTTP_X_FORWARDED_FOR"), "unknown"))
    $ip = getenv("HTTP_X_FORWARDED_FOR");
 
  elseif (getenv("REMOTE_ADDR") && strcasecmp(getenv("REMOTE_ADDR"), "unknown"))
    $ip = getenv("REMOTE_ADDR");
 
  elseif (!empty($_SERVER['REMOTE_ADDR']) && strcasecmp($_SERVER['REMOTE_ADDR'], "unknown"))
    $ip = $_SERVER['REMOTE_ADDR'];
 
  else
    $ip = "unknown";
 
  return($ip);
}