On another forum I found that Black Ops requires the following ports.
Black Ops itself, it requires TCP ports 3074 and 27014-27050. The specific UDP ports for Black Ops are 3074, 3478-4380, and 27000-27030
Now I personally have not had any problems with Black Ops. But you may need to go into the router and set up port forwarding. Now these ports are for the PC version, anyone on a PS3 or Xbox, it may be different.