Re: igmp: Staggered igmp report intervals for unsolicited igmp reports

On Thu, 23 Sep 2010, Jason Gunthorpe wrote:

quoted

IPoIB creates a infiniband multicast group via the IB calls for a IP
multicast group. Then IGMP comes into play and the kernel sends the IP
based igmp report. This igmp report must be received by an outside router
(on an IP network) in order to for traffic to get forwarded into the IB
fabric. You can end up with a IB multicast configuration that is all fine
but with loss of the unsolicited packets due to fabric reconfiguration not
being complete yet. The larger the fabric the worse the situation.

But my point is that IB has very limited multicast, if I create a IB
group and then send IGMP into that group *it will not reach a router*.

The IPoIB routers automatically join all IP MC groups created.

The only way this kind of scheme could work is if an IGMPv2 IPoIB
router listens for IB MGID Create notices from the SA and
automatically joins all groups that are created, so it can get IGMPv2
membership reports. Which obviously adds more delay, lag, and risk.

Right that is how it works now.

I'm *guessing* that the change in IGMPv3 to send reports to 224.0.0.22
(all IGMPv3 multicast address) is related to this sort of problem, and
it seems like on IB IGMPv2 is not a good fit and should not be used if
v3 is available..

Existing routers do no support IGMPv3.

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