[c-nsp] Multicast between VRFs within a single router, probably an ASR9K

[John Neiberger]

I have a lab situation where we would really benefit from being able
to get multicast receivers in one VRF to join multicast sources in a
different VRF, all on the same router, probably an ASR9K. We've
thought of a couple ways to do this. One is to offload the source VRF
to another box and then use subinterfaces on the trunk links with each
subinterface in a different VRF. That would work just fine, but it
would mean that each new receiver VRF would increase the bandwidth
usage on the trunk. We'd end up with the same multicast streams being
duplicated several times over on those links.

Another method would be to just run cables between the VRFs. That
would work well, but it would eat up ports quickly, especially since
we'll probably need a few gig per VRF.

I'd really like to find a way to do this within the box. I've already
gotten unicast to work by using BGP to redistribute between the VRFs
in a sort of VRF Lite configuration. However, I can't get multicast to
work across the VRF boundaries. MDT doesn't seem like an option
because I'm not doing mpls and this is all happening within one box,
not from PE to PE or anything like that, and we're trying to go from
one VRF to another, which I don't think MDT would allow us to do.

It sure seems like there should be a way to make this work, but I'm
not that familiar with VRFs, and I'm definitely not that familiar with
trying to do multicast across VRFs. In the end, we don't even need
unicast redistribution at all. We want to have separate VRFs for each
virtual lab, and those VRFs just need to be able to pull multicast
sources from the source VRF. There will be no unicast traffic at all.

This is purely for a lab environment at work for testing various video
encoding/compression systems. We wouldn't be thinking of attempting
this in a production environment, but it sure would solve some
problems for us if we could pull it off in the lab area.

Any thoughts?

Thanks!
John