When you attempt to play games on your XBox 360, you might be warned that you are behind a "Strict NAT" and unable to use all the functions of the game. While behind a strict NAT, Microsoft says you might experience the following:
- You cannot hear a certain player within a game or someone cannot hear you
- You cannot join a party or your friend cannot join your party
A NAT (stands for Network Address Translation) is a device that takes a public IP address and splits it amongst multiple private IP addresses (say, 10.whatever, 192.168.whatever, or 172.whatever). At your home, this is likely built in to your wireless router, and your Xbox is allowed to communicate to the router and open ports on a whim.
However, at USD and many college campuses, we use commercial routers that handle communication for thousands of computers. For security and design reasons, these routers cannot have ports automatically opened like personal routers do. Since your XBox 360 might have a different IP every day, it's not even possible to manually open these ports for your device.
While it might keep you from connecting to certain parties, Microsoft says "NAT problems do not affect game play speed".
(Portions of this KB are from Microsoft's Xbox Support)