IP地址： Internet協(xié)議地址（IP地址）是分配給連接到使用Internet協(xié)議進行通信的計算機網(wǎng)絡的每個設備的數(shù)字標簽。IP地址有兩個主要功能：主機或網(wǎng)絡接口標識和位置尋址。

$_SERVER['REMOTE_ADDR']：瀏覽當前頁面的用戶計算機的ip地址

$_SERVER['HTTP_CLIENT_IP']：客戶端的ip（推薦學習：PHP編程從入門到精通）

$_SERVER['HTTP_X_FORWARDED_FOR']：瀏覽當前頁面的用戶計算機的網(wǎng)關

$_SERVER['HTTP_X_REAL_IP']：nginx 代理模式下，獲取客戶端真實IP

/**  * 獲取客戶端IP地址  */ function real_ip() {   $ip = $_SERVER['REMOTE_ADDR'];   if (isset($_SERVER['HTTP_X_FORWARDED_FOR']) && preg_match_all('#d{1,3}.d{1,3}.d{1,3}.d{1,3}#s',    $_SERVER['HTTP_X_FORWARDED_FOR'], $matches)) {     foreach ($matches[0] AS $xip) {       if (!preg_match('#^(10|172.16|192.168).#', $xip)) {         $ip = $xip;         break;       }     }   } elseif (isset($_SERVER['HTTP_CLIENT_IP']) && preg_match('/^([0-9]{1,3}.){3}[0-9]{1,3}$/',    $_SERVER['HTTP_CLIENT_IP'])) {     $ip = $_SERVER['HTTP_CLIENT_IP'];   } elseif (isset($_SERVER['HTTP_CF_CONNECTING_IP']) && preg_match('/^([0-9]{1,3}.){3}[0-9]{1,3}$/',    $_SERVER['HTTP_CF_CONNECTING_IP'])) {     $ip = $_SERVER['HTTP_CF_CONNECTING_IP'];   } elseif (isset($_SERVER['HTTP_X_REAL_IP']) && preg_match('/^([0-9]{1,3}.){3}[0-9]{1,3}$/',    $_SERVER['HTTP_X_REAL_IP'])) {     $ip = $_SERVER['HTTP_X_REAL_IP'];   }   return $ip; }