netfilter & multicast

[Giacomo Mulas <gmulas@ca.astro.it>]

	I have a problem with firewalling and multicast traffic.

The setup: basic iptables-based firewall configured basically to let
anything from the protected LAN out to the internet and let only
ESTABLISHED,RELATED back in. Of course there are the obvious exceptions to
let through DNS requests to our authoritary name server etc., but this is
not relevant. All in all, this firewall works like a charm for any unicast
traffic.

The problem: netfilter does not seem to recognise and properly let through
multicast traffic or, more likely, I did not properly configure it to do
so.

To simplify things, I also tried with a bare bones iptables script on my
laptop, just configured to let anything out and only ESTABLISHED,RELATED
back in. Everything seems to be working properly as far as unicast is
concerned, but I just cannot see multicast groups unless I turn off
firewalling.

Is there anyone with a working firewalling setup (I mean, working well
with multicast) who would share some of his wisdom on this? I would
appreciate even a RTFM answer, as long as a pointer to an appropriate "FM"
is suggested...

-- 
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Giacomo Mulas <gmulas@ca.astro.it, giacomo.mulas@tin.it>
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