[openib-general] IPv6 and IPoIB scalability issue

[Jason Gunthorpe]

On Fri, Dec 01, 2006 at 03:07:23PM -0500, Hal Rosenstock wrote:

> > configuration of MGID space in SM to consider for compression may
> > be required total of 2005 MGIDs in cluster up to 2005 multicast
> > subscriptions per node (sender only for Solicited Node initiators)
> 
> Does the node subscribe to every IPv6 SN group ?

A node will only use another nodes SN group in a send-only fashion and
only when it is doing neighbour discovery for that node.

So at the worst case you potentially have N^2 send-only subscriptions,
N normal subscriptions and N groups.

If IPv6 SN multicast MLIDs are always routed in the fabric so that all
IPv6 nodes can be send-only then the send-only subscriptions don't
need to be considered. Presumably because of this send-only join and
unjoin can result in no data structure in the SM..

> I think before pursuing option 1 there needs to be a discussion with the
> IETF WG involving the RFC authors (Vivek Kashyap, Jerry Chu).

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

Another approach would be to manipulate the IPv6 address of the node
so that the lower 24 bits are the same. That gets the same effect, but
I'm not sure how you'd go about doing it :>

Jason