[plug] ADSL Firewall, IP masq and games

[Alan Graham]

Hi people, new to the list and to plug, hope to get to the next meeting.

I've had ADSL through iinet for a couple of months now, and I'm almost there
with my firewall setup, but there are a couple of games that I can't get
working through the firewall, viz Tribes 2 and Grand Prix Legends.  Both use
UDP at least initially, for server discovery and the like.

The firewall is based on RH 7.0, kernel 2.2.16, with almost everything switched
off, running Bastille to get my base ipchains ruleset. 

Switching off all chains, bar masq. on the forward chain (ie, input and output
to 'accept') and everything works fine.  Restarting the chains, and I see the
udp calls from the games coming into the internal interface, and going out
(masq'ed) on the external, and I also see the responses from the servers coming
in on the external interface.  But they never appear going out of the internal
interface back to the client.  I'm using ethereal with tcpdump to monitor the
traffic.

At first, I thought there was a kernel problem, eg, loose udp not on or
something, but then I remembered that everything works with just masquerading
on.  I'm assuming that tcpdump sees packets after filtering, so the udp
responses are getting in ok.  But I can't find anything that would stop
these going out on the internal network.

Any suggestions as to what I can try next would be gratefully appreciated, I'm
running out of ideas.

Thanks heaps

Alan Graham