More information:
Before I could send and receive chat, but I could not see other players moving nor could they see me. This seems to imply that TCP packets are sent and received correctly. I then tried setting a DMZ on my router and now I can see other players moving, but they cant see me (ie UDP is received correctly but not sent). Anyone know what kind of misconfiguration could lead to this situation? Thanks.

Edit: Also, it seems to work fine when I use the -connect option