如果用户使用了代理服务器，真实ip就不在HTTP_CLIENT_IP头中，而需要通过http头HTTP_X_FORWARDED_FOR来解析了。

如下php函数：

<? 
function GetIP() { //获取IP 
    if ($_SERVER["HTTP_X_FORWARDED_FOR"]) 
        $ip = $_SERVER["HTTP_X_FORWARDED_FOR"]; 
    else if ($_SERVER["HTTP_CLIENT_IP"]) 
        $ip = $_SERVER["HTTP_CLIENT_IP"]; 
    else if ($_SERVER["REMOTE_ADDR"]) 
        $ip = $_SERVER["REMOTE_ADDR"]; 
    else if (getenv("HTTP_X_FORWARDED_FOR")) 
        $ip = getenv("HTTP_X_FORWARDED_FOR"); 
    else if (getenv("HTTP_CLIENT_IP")) 
        $ip = getenv("HTTP_CLIENT_IP"); 
    else if (getenv("REMOTE_ADDR")) 
        $ip = getenv("REMOTE_ADDR"); 
    else 
        $ip = "Unknown"; 
    return $ip; 
} 
?>