Multicast into intranet+

[Andreas Tannert]

Hi,

i have a small intranet with 3 computers. One of these (hostname is
GATE) has two ethernetcards, runs redhat and does the masquerading and
packet filtering for all connections using ipchains. Everything works
fine, but the problem is, that i can't receive any multicast packet
inside the intranet. On GATE i recieve the multicat packets on eth0,
which ist the interface to the internet. On eth0 i can see these packets
using tcpdump while on eth1 (interface to intranet) nothing happens. I
have tried to forward the incoming multicast packets using the
forward-chain of ipchains. But these packet don't reach the section of
ipchains. I set up a trivial rule for the input chain to inspect,
whether packets will be filtered.

#> ipchains -A input -p udp -j ACCEPT -l

And the input chain used this rule and wrote a lot of log. Multicast
packets are handled by this rule. So i tried the same on the forward
chain.

#> ipchains -A forward -p udp -j ACCEPT -l

But nothing happens. I found some dns requests in the logfile, but no
multicast requests. I changed the rule to deny all except DNS.

#> ipchains -A forward -p udp --dport ! 53 -j DENY -l

But like before no multicast packets were filtered. I don't know, what
happens to these packets. Ohter udp connections like DNS work fine.

What else can i do, to forward multicast packets into the intranet.

Any tips are welcome.

Thanks.

Andreas