Multicast & iptables

[Ferry Huberts]

Hello guys & gals

I have a question w.r.t. multicast and iptables for a very 'unique'
application. It's a kind of 'box in the middle' application.
So that you're warned :-)

I have a userspace application opening a socket on the external interface
and subscribing itself to a multicast address.

When the box receives a packet addressed to itself on its internal
interface, it does a PREROUTING/DNAT to the multicast address and a
POSTROUNTING/SNAT to its external interface.

When the box receives a packet addressed to itself on its external
interface, it does a PREROUTING/DNAT to the internal default gateway for
multicast and a POSTROUNTING/SNAT to its internal interface.

I do have ip_forwarding on 1 in /proc :-)

However, this does not seem to work :-(
When I sniff traffic I do see that IGMP is ok, so my userspace app. is
doing ok, but I don't see the NATted traffic at all.
Are multicast addresses 'blocked' by iptables or am I making a mistake here?

much appreciated

Ferry Huberts