I have forwarded ports for torrenting before, but just wondering, for MVC3, what ports should I forward? And how? (TCP, UDP, etc.)
Xbox Live? PSN?
Generally speaking, Port Forwarding Guides Listed by Manufacturer and Model - PortForward.com is a great tool to help walk you though how to set up port forwarding.
Another way to do it would be to add your ps3/360 to the DMZ so that no ports are blocked.
Most routers these days don’t need to have anything done on the firewall to get out to fight on the t’interwebs. If this isn’t the case for you, it’s worth a look around to see if your router has support for uPnP - that certainly works for me. [I’m guessing that you have problems with your router else you wouldn’t be asking the question]
Finally, if neither of the above works, a lot of routers have a pre-set of rules for PS3 and XBox, which you can get to from the NAT or Firewall sections.
What router do you have?