[openib-general] IPv6 and IPoIB scalability issue

[Jason Gunthorpe]

On Fri, Dec 01, 2006 at 11:20:15AM -0500, Hal Rosenstock wrote:
> > For IPv6 only the lower 24 bits of each assigned IPv6 address are
> > used to construct a solicited node multicast in the range 
> > FF02::1:FF00:0/104. The Solicited Node Multicast address it not
> > expected to be uniquely subscribed.
> 
> Any idea on how many would subscribe ? What does this depend on ?

Each node subscribes to a SNM on an interface for each IPv6 address on
that interface. In most cases that should mean 1 subscription per
interface, but more is possible..

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..

Here is another thought.. Is there anything in the spec that says a
MGID must map to a MLID? If there is a single subscription why not
just do away with the MLID and return a unicast LID of the only
subscriber? That would probably solve 90% of the IPv6 issue Todd
pointed out. MGID compression would take care of the rest..

Jason