May I know how to close my port 113 ??

Port 113 Ident

You can block 113 IF your router uses NAT and has Port Forwarding. Access your router control interface and set up Port Forwarding so all TCP & UDP requests for port 113 get forwarded to an IP address in your LAN range. This IP address should be an IP that will never get asigned to any computer, preferably an ip at the end og the range.

For instance:

If your IP range is 192.168.1.1 - 192.268.1.255, then forward all port 113 requests to the IP number of 192.168.1.250. When a request comes in, the router will try to forward the request to that IP and when it detects that no computer exists there, it will drop the request and will not reply back to the originating requester IP, thus stealthing that port.

 

This trick of port forwarding to stealth port 113 IS covered at Gibson'd site:

https://grc.com/port_113.htm