[openib-general] IPv6 and IPoIB scalability issue

[Hal Rosenstock]

On Thu, 2006-11-30 at 17:41, Todd Rimmer wrote:
> > From: Roland Dreier [mailto:rdreier at cisco.com]
> > Sent: Thursday, November 30, 2006 5:32 PM
> > To: Todd Rimmer
> > Cc: openib-general at openib.org
> > Subject: Re: [openib-general] IPv6 and IPoIB scalability issue
> > 
> >  > Proposed solution:
> >  > - add an IPoIB configuration parameter.  This parameter could
> redirect
> >  > the Solicited Node Multicast traffic to the IPv6 All Nodes
> multicast
> >  > address (IB GID 0xff01601B.....0000001)
> > 
> > This is silly however.  For one thing you are now not following the
> > RFC, and compliant IPv6 over IPoIB stacks will send neighbour
> > discovery messages to the solicited node address, so they won't be
> > received since the node didn't join.
> > 
> > There's no requirement that a SM assign a unique MLID to each
> > multicast group.  The obvious solution to the problem is simply that
> > the SM reuse MLIDs for solicited node multicast groups, perhaps even
> > collapsing all of them down to 1 MLID.
> > 
> 
> I think its worth discussing a number of alternatives.  I'm not sure
> there is an ideal solution here.
> 
> Doesn't an SM based solution produce other complications?
> - Such as the SM/SA must maintain an extremely large list of Multicast
> Member records (potentially N^2).

Certainly O(N) groups where N is the number of IPv6 hosts (and each
group is 1 or more MCMs).

> - Host nodes will be joining N multicast groups and maintaining
> membership in them (potentially further stressing the SA, etc)

Do all IPv6 nodes join all the solicited node groups ? I don't see this
occuring (so far) on the subnets I have seen.

> Not to mention that the SM would then need to know about IPoIB GID
> addressing conventions (which seems like a violation of network layers,
> etc).

There's already the IPv6 signature as part of the MGID to help with this
layering violation. Some SMs already do things with this already.

-- Hal

> Todd Rimmer
> 
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