I stumbled across this site when looking for the JJ2 patch and some levels, and was rather suprised as to how strong the JJ2 community appeared to be (hadn't been able to find anything since J2C closed down). So I went on a level-downloading rampage, and then tried online games (after finding the list server patch). Every time I've tried so far, I stay connected for about 30 seconds before getting booted off by the server.

I *do* know about networking, and so did some digging of my own. Rough network outline: my PC is connected thru a wireless network to a router/NAT box with a DSL modem. I have a firewall on my PC (Norton), and that has the required ports for Jazz open (UDP to/from 10052, TCP to/from 10052, TCP to 10053 + 10054). The NAT box is forwarding packets properly - I can see in a packet sniffer the return UDP packets from the pings and status requests.

What appears to happen is that Jazz gets the server list, pings each server and gets a reply, and continues to ping until I connect to one. It then opens a TCP connection to 10052, and starts to send lots of UDP packets to 10052 as well. I don't get any replies to those packets (unlike the ones earlier), and then after 30 seconds the server boots me. All the TCP stuff behaves, and inside of the game I see chat messages (and have been able to send them as well).

It seems to me that forwarding ports should only be necessary if you are hosting a server, and other games work fine (UT & Half-life for examples). And the NAT box is forwarding the replies to the initial server query packets.
So, um, any ideas, folks? A virtual bit o' chocolate to the one who solves the problem