//获得客户端IP
public static function getIp()
    {
        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;
    }

文章题目：PHP获得客户端IP
文章起源：http://scyanting.com/article/gghoej.html