REMOTE_ADDR 是你的客戶端跟你的服務器“握手”時候的IP。如果使用了“匿名代理”，REMOTE_ADDR將顯示代理服務器的IP。
HTTP_CLIENT_IP 是代理服務器發送的HTTP頭。如果是“超級匿名代理”，則返回none值。同樣，REMOTE_ADDR也會被替換為這個代理服務器的IP。
$_SERVER['REMOTE_ADDR']; //訪問端（有可能是用戶，有可能是代理的）IP
$_SERVER['HTTP_CLIENT_IP']; //代理端的（有可能存在，可偽造）
$_SERVER['HTTP_X_FORWARDED_FOR']; //用戶是在哪個IP使用的代理（有可能存在，也可以偽造）

下面是測試代碼：

服務端獲取IP地址 http://ip.VeVb.com/ 其代碼如下:

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

客戶端代碼：
偽造IP測試：

$url = ‘http://ip.VeVb.com/’;
$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/1.1/n”;
$request.=”Host: “.$URL_Info["host"].”/n”;
$request.=”Referer: “.$URL_Info["host"].”/n”;
$request.=”Content-type: application/x-www-form-urlencoded/n”;
$request.=”X-Forwarded-For:192.168.1.4/n”;//HTTP_X_FORWARDED_FOR的值
$request.=”client_ip:192.168.1.5/n”;//HTTP_CLIENT_IP的值
$request.=”Content-length: “.strlen($data_string).”/n”;
$request.=”Connection: close/n”;
$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;

輸出：

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測試：

$cUrl = curl_init();
curl_setopt($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;

輸出：

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