FWSM multi-context doesn't do multicast. So I'm attempting to doit the same way as you'd configure non-ip protocols like decnet.
I have put a vlan interface into the vlan, but with an unnumbered ip address
ip unnumbered loopback 0
and the normal IP route TO vlan123 is via the FWSM (In the same chassis).
Multicast is working fine from the core networks TO the vlan, I can see packets arriving at the hosts. But packets TO the group address FROM hosts on vlan123 get dropped at the router, with 'not RPF interface'.
Now I should eb able to override that with a static mroute... But I can't get a static mroute to behave as an INTERFACE route. It always wants a REMOTE IP address to uise as the neighbour.
Is there a better way? (I was thinking of using a VRF and tunnelling, but I'd like to keep the config as simple as possible).