[openib-general] IPv6 and IPoIB scalability issue

[Todd Rimmer]

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

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).

Todd Rimmer