Linux IP Masquerading supports peer-to-peer UDP games
as of kernel 2.1.131ac11, thanks to a patch from Juanjo.
Any UDP peer-to-peer game that uses the technique outlined at
should work behind a Masqerading host runing 2.1.131ac11
or later without any special port forwarding. This
should be a big improvement over current practice-
users and NAT developers will no longer need to write
or load special code for each game.
The first games known to use this technique
are Heavy Gear 2 Demo and Battlezone, and they
may require an update (see the above URL).
DirectPlay does not yet support this technique, but
there is at least one game networking API that does,
so it's likely that more games will use this technique
in the future.
Speaking only for myself, not for my employer