SYMPTOMS:

If you are having difficulties hosting a Neverwinter Nights 2 internet
multiplayer game from behind a router, try opening up these ports in your
router settings.

RESOLUTION:
Please consult your router's manual for instructions on port forwarding.

Neverwinter Nights 2 uses UDP port forwarding.

These are the ports to be opened:

3658
3659
3660
6500
27900
28910
5120
5300

Please consult your network administrator or your router manufacturer for
information on how to set up these ports. You should also install the latest
firmware available for your router from the manufacturer.

Opening Ports to Play Behind a Firewall
The following ports may need to be opened for GameSpy servers to see the
game: 3658, 3659, 3660, 6500, 27900, 28910
GameSpy Arcade may also need the following TCP ports open in order to
function properly:
- 6667 (IRC)
- 3783 (Voice Chat Port)
- 27900 (Master Server UDP Heartbeat)
- 28900 (Master Server List Request)
- 29900 (GP Connection Manager)
- 29901 (GP Search Manager)
- 13139 (Custom UDP Pings)
- 6515 (Dplay UDP)
- 6500 (Query Port)
You will also need to open the server port (5121 by default) and the
following port for the game stats to be updated correctly: 29920 (Gamestats
Server)"