1、ThinkPHP5通过助手函数即可获取

request()->ip()

2、通过自己解析

function get_client_ip($type = 0)
{
    $type = $type ? 1 : 0;
    static $ip = NULL;

    if ($ip !== NULL) {
        return $ip[$type];
    }

    if (isset($_SERVER['HTTP_X_REAL_IP'])) {
        //nginx 代理模式下，获取客户端真实IP
        $ip = $_SERVER['HTTP_X_REAL_IP'];
    } elseif (isset($_SERVER['HTTP_CLIENT_IP'])) {
        //客户端的ip
        $ip = $_SERVER['HTTP_CLIENT_IP'];
    } elseif (isset($_SERVER['HTTP_X_FORWARDED_FOR'])) {
        //浏览当前页面的用户计算机的网关
        $arr = explode(',', $_SERVER['HTTP_X_FORWARDED_FOR']);
        $pos = array_search('unknown', $arr);
        if (false !== $pos) unset($arr[$pos]);
        $ip = trim($arr[0]);
    } elseif (isset($_SERVER['REMOTE_ADDR'])) {
        //浏览当前页面的用户计算机的ip地址
        $ip = $_SERVER['REMOTE_ADDR'];
    } else {
        $ip = $_SERVER['REMOTE_ADDR'];
    }
    // IP地址合法验证
    $long = sprintf("%u", ip2long($ip));
    $ip   = $long ? array($ip, $long) : array('0.0.0.0', 0);
    return $ip[$type];
}

参考
获取客户端IP地址