[openib-general] IPv6 and IPoIB scalability issue

[Hal Rosenstock]

On Fri, 2006-12-01 at 14:24, Jason Gunthorpe wrote:
> On Fri, Dec 01, 2006 at 01:53:45PM -0500, Hal Rosenstock wrote:
> > > Generally IPv6 addresses should be constructed based on the EUI64 of
> > > the IB interface. In this case the lower 24 bits of the SNM will be
> > > the lower 24 bits of the EUI64. Thus in many cases the SNMs will be
> > > cluster-unique..
> > 
> > It seems to depend on the low 24 bits of the IPv6 addresses in the
> > subnet being the same (as to whether there is more than 1 member of
> > these groups).
> 
> Correct. It is common practice for all IPv6 addresses to have the
> lower 64 bits be the EUI64 of the interface. The administrator can
> assign a different address, but that could be discouraged for
> scalability reasoons.
> 
> > > Here is another thought.. Is there anything in the spec that says a
> > > MGID must map to a MLID?
> > 
> > Yes. Here's the first one:
> > p.149 line 3-8
> 
> Hmm. Thats a shame.

I think there are other issues with this and haven't thought about it
enough. What happens if a second node joins that group (as the low 24
bits match) ? How would the LID be revoked and changed to an MLID ?
There's more spec checking to do here...

>  It is a conformance statment too :< At least the
> accepetance statements in C9 page 279+ don't specify to check that a
> MGID is matched with a MLID

I would say that's a hole in the spec right now...

>  so at least it should work with current
> hardware.

I would use the word might rather than should in that last sentence.

-- Hal

> Jason