The port in the router can't be closed, but it can be set so that even the router's computer can't get online. The method is as follows:

1. Only the MAC address of 00-11-22-33-44-55 is allowed to connect to the external network.

2. Change the MAC address of the computer allowed to access the external network to 00-11-22-33-44-55, so that the computer allowed to access the external network can also connect.

It is best to record the original MAC address of each computer before modifying the MAC address of the computer, and don't give the user the right to modify the MAC address himself or let the user know, otherwise everyone will be in trouble.

4. The method of modifying the MAC address:

Local Area Connection-Properties-Configuration-Advanced

Just fill in the MAC address 00 1 122334455 in the network address.

There is no conflict between 5.5. MAC address, but only if the IP address is the same. Just set the IP address to static.