you can access the network switch/modem and block the systems by IP Address.
First you have to set the IP addresses of the systems you want to block.
then access the administrator menu of the router/modem. You can do it by typing in the address bar, the modem/router's IP address. D-link IP Address would be 192.168.1.1
from the left pane, choose MANAGEMENT - then ACCESS CONTROL - IP ADDRESSESS.
add the IP Addressess you want to block.
then enable ACCESS CONTROL MODE and you are done