Nginx禁止ip访问或非法域名访问

server {
   listen 80 default_server;
   server_name _;
   return 501;
}

server {
  listen 80 default_server;
  server_name _;
  rewrite ^(.*) Http://www.jb51.com/$1 permanent;
}　

if ($host ~ '^www.jb51.com'){
     return 301 https://www.jb51.net$request_uri;
   }

server {undefined
    listen 80 default_server;
    server_name _;
    return 501;
}