nginx 如何禁止 ip 直接访问

原谅我网上教程没看懂
server {
listen 80 default_server;
server_name _;
return 444;
}
server {
listen 80 ;
server_name xxx.xxx;

# Handle all locations
location / {
# Pass the request to Gunicorn
proxy_pass http://127.0.0.1:8000;
proxy_redirect off;

# Set some HTTP headers so that our app knows where the
# request really came from
proxy_set_header Host $host;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
server 加上 default_server 后报错
nginx: [emerg] a duplicate default server for 0.0.0.0:80 in /etc/nginx/nginx.conf:47
nginx: configuration file /etc/nginx/nginx.conf test failed
如果不加那么没效果
去掉第一个 server 直接访问 ip 会出现 Welcome to nginx 页面

求助，环境是 python+flask+gunicorn+nginx