[rbridge] IP Multicast groups/ layer 2 or layer 3?

[Radia Perlman]

When an RBridge  R announces via IS-IS which IP multicast groups are  
reachable on R's directly
attached links, should the groups be layer 3 or layer 2 addresses?

If it's layer 3, then there will have to be separate announcements for 
IPv4 and IPv6 groups.
If it's layer 2, then 32 IPv4 groups would map to the same layer 2 
multicast address (and I'm
not sure what it is for IPv6).

I don't care. The spec currently says layer 2, but there is a question 
in the spec asking if that's what
we really want.

Radia