[clug] Joining a multicast stream from a firewall

[Brett Worth]

I've reached (and exceeded) my IP knowledge and need some help.

I regularly join and utilise a multicast stream from machines on my home
network.  These packets look like this on my network:

21:36:06.112240 IP 192.168.6.100.lm-webwatcher > 239.193.0.96.lm-webwatcher: UDP, length: 1316
21:36:06.113660 IP 192.168.0.1.lm-webwatcher > 239.193.0.2.lm-webwatcher: UDP, length: 1316
21:36:06.114595 IP 192.168.6.100.lm-webwatcher > 239.193.0.96.lm-webwatcher: UDP, length: 1316
21:36:06.115033 IP 192.168.0.1.lm-webwatcher > 239.193.0.2.lm-webwatcher: UDP, length: 1316
21:36:06.116677 IP 192.168.6.100.lm-webwatcher > 239.193.0.96.lm-webwatcher: UDP, length: 1316
21:36:06.117177 IP 192.168.0.1.lm-webwatcher > 239.193.0.2.lm-webwatcher: UDP, length: 1316

I also have a machine that's handling my pppoe connection which I'd also like to have use the
multicast stream.  When I ask mplayer or xine to join the stream from this machine is appears
to join the stream but never sees any of the multicast packets.   The output files stay at zero
length.

I have a feeling that its because the source address on the initial packets is going out as the
dsl0 address and not the eth0 address i.e. the default route.  If this seems reasonable then 
is there a way to fix it? 

-- 
Brett