[openib-general] IPv6 and IPoIB scalability issue

[Hal Rosenstock]

On Fri, 2006-12-01 at 16:47, Jason Gunthorpe wrote:
> 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.

Send only subscriptions are largely the same (in terms of SM/SA) as full
subscriptions except in a couple of details.

> 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..

There is a data structure associated with these memberships.

-- Hal

> > 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