[openib-general] IPv6 and IPoIB scalability issue

[Roland Dreier]

 > Option 1 sounds difficult to me. It would be hard to have interop
 > between nodes using this optimization and nodes that don't..

Yes, that is a major problem.

One intermediate thing we could do is to have nodes join their own
solicited-node group as a full member, but have other nodes send ND
messages to the all-nodes group.  Then the SM would only have O(N)
MCG memberships to maintain.  But it still requires the SM to be smart
about mapping multiple MCGs to a single MLID.

And even if that works, I'm not sure it's compliant with all the
relevant RFCs, and it might break in some strange situations...

(To be honest though, I think that the SM for a subnet with N nodes
should really be beefy enough to handle N^2 multicast memberships.
Even 10K nodes leads to only 100M group memberships, which shouldn't
be _that_ expensive with the right data structures)

 - R.