[ewg] [PATCH] Make multicast and path record queue flexible.

Christoph Lameter cl at linux.com
Tue Oct 5 13:43:47 PDT 2010

On Tue, 5 Oct 2010, Jason Gunthorpe wrote:

> > > I still think the problem you have with IGMPv2 is best solved by
> > > leaning on the gateway vendors to support IGMPv3 - which *does* send
> > > all reports to
> >
> > s/22/2
> No, 22. RFC 3376:
> 4.2.14. IP Destination Addresses for Reports
>    Version 3 Reports are sent with an IP destination address of
>, to which all IGMPv3-capable multicast routers listen.  A
>    system that is operating in version 1 or version 2 compatibility
>    modes sends version 1 or version 2 Reports to the multicast group
>    specified in the Group Address field of the Report.  In addition, a
>    system MUST accept and process any version 1 or version 2 Report
>    whose IP Destination Address field contains *any* of the addresses
>    (unicast or multicast) assigned to the interface on which the Report
>    arrives.

Argh. Another MC group. And the ib layer does need to do IB level joins
for those. So the initial messages will be lost for the first join(s)?

> > Certainly a solution for the igmp messages themselves but not for
> > initial traffic or traffic send via sendonly join.
> Using .22 will generally solve the problems with sychronizing the
> IPoIB gateway to the state of the IGMPv3 clients. Yes, there will
> still be some unknown lag in building the IB side of the network and
> for the router(s) to get ready to handle the group - but at least it
> is no longer dependent on any timeouts.

How do you propose to handle the IB level join to to avoid
packet loss there? IGMP messages will still get lost because of that.

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