I have a 7206 vxr router with a dual 10/100 ethernet port. I just found out that I'll need an extra port on a router. can i buy a separate appliance with gigaethernet port(s) and connect on an empty slot? how is that appliance called?
You can try the 7200 Port Adapter (Cisco Part number PA-GE). However, these are fiber ports and require to have GBIC installed. You will need to have NPE-300 or above processor.
If you only need 100Mb copper ports, you can try PA-2FE-TX.