HTTP_CLIENT_IP：可通过http头伪造
HTTP_X_FORWARDED_FOR：可通过http头伪造
REMOTE_ADDR：可能是用户真实IP也可能是代理IP

服务端获取IP地址 http://www.taoyiz.com/util/ip 其代码如下:

$s_onlineip = getenv(‘HTTP_CLIENT_IP’);
echo “HTTP_CLIENT_IP:”.$s_onlineip.”
n”;
$s_onlineip = getenv(‘HTTP_X_FORWARDED_FOR’);
echo “HTTP_X_FORWARDED_FOR:”.$s_onlineip.”
n”;
$s_onlineip = getenv(‘REMOTE_ADDR’);
echo “REMOTE_ADDR:”.$s_onlineip.”
n”;
$s_onlineip = $_SERVER['REMOTE_ADDR'];
echo “$_SERVER['REMOTE_ADDR']:”.$s_onlineip.”
n”;

客户端代码：
伪造IP测试：

$url = ‘http://www.taoyiz.com/util/ip’;
$data_string = ‘test=test’;
$URL_Info    =    parse_url($url);
$request = ”;
if (!isset($URL_Info["port"]))
$URL_Info["port"]=80;
$request.=”POST “.$URL_Info["path"].” HTTP/1.1n”;
$request.=”Host: “.$URL_Info["host"].”n”;
$request.=”Referer: “.$URL_Info["host"].”n”;
$request.=”Content-type: application/x-www-form-urlencodedn”;
$request.=”X-Forwarded-For:192.168.1.4n”;//HTTP_X_FORWARDED_FOR的值
$request.=”client_ip:192.168.1.5n”;//HTTP_CLIENT_IP的值
$request.=”Content-length: “.strlen($data_string).”n”;
$request.=”Connection: closen”;
$request.=”n”;
$request.=$data_string.”n”;

$fp = fsockopen($URL_Info["host"] $URL_Info["port"]);
fputs($fp $request);
$result = ”;
while(!feof($fp)) {
$result .= fgets($fp 1024);
}
fclose($fp);
echo $result;

输出：

HTTP_CLIENT_IP:192.168.1.5
HTTP_X_FORWARDED_FOR:192.168.1.4
REMOTE_ADDR:127.0.0.1
$_SERVER['REMOTE_ADDR']:127.0.0.1

代理IP测试：

$cUrl = curl_init();
curl_setopt($cUrl CURLOPT_URL $url);
curl_setopt($cUrl CURLOPT_RETURNTRANSFER 1);
curl_setopt($cUrl CURLOPT_HEADER 1);
curl_setopt($cUrl CURLOPT_USERAGENT “Mozilla/99.99″);
//curl_setopt($cUrl CURLOPT_TIMEOUT 10);
curl_setopt($cUrl CURLOPT_PROXY ’125.77.194.103:80′);
$c = curl_exec($cUrl);
curl_close($cUrl);
echo $c;

输出：

HTTP_CLIENT_IP:
HTTP_X_FORWARDED_FOR:
REMOTE_ADDR:125.77.194.103
$_SERVER['REMOTE_ADDR']:125.77.194.103