Thank you for your responses.
Of course, the difficult part was isolating it through its fixed IP or MAC address so I wouldn't have to dedicate a router port just for that or isolate everything on the switch. However, I think I won't have any other choice but to use additional hardware or...
I have ASUS Merlin Firmware: 3004.388.8_2, and I have a device connected via Ethernet to a switch, and the switch is connected to the router. I want this device to have no access to the rest of my local network. Is this possible?
Thank you very much.