From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Lameter Subject: Re: igmp: Staggered igmp report intervals for unsolicited igmp reports Date: Thu, 23 Sep 2010 12:37:28 -0500 (CDT) Message-ID: References: <20100922215052.GK11157@obsidianresearch.com> <20100923172603.GM11157@obsidianresearch.com> Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Cc: David Stevens , linux-rdma-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Bob Arendt To: Jason Gunthorpe Return-path: In-Reply-To: <20100923172603.GM11157-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org> Sender: linux-rdma-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: netdev.vger.kernel.org On Thu, 23 Sep 2010, Jason Gunthorpe wrote: > On Thu, Sep 23, 2010 at 10:32:17AM -0500, Christoph Lameter wrote: > > > > Is the issue you are dropping IGMP packets because the 224.0.0.2 join > > > hasn't finished? Ideally you'd wait for the SA to reply before sending > > > a IGMP, but a simpler solution might just be to use the broadcast MLID > > > for packets addressed to a MGID that has not yet got a MLID. This > > > would bebe similar to the ethernet behaviour of flooding. > > > > IGMP reports are sent on the multicast group not on 224.0.0.2. 224.0.0.2 > > is only used when leaving a multicast group. > > Hm, that is quite different than in IGMPv3.. How does this work at all > in IB? A message to the multicast group isn't going to make it to any > routers unless the routers use some other means to join the IB MGID. 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. If all unsolicited igmp reports are lost then the router will only start forwarding the mc group after the reporting intervals (which could be in the range of minutes) when it triggers igmp reports through a general igmp query. Until that time the MC group looks dead. And people and software may conclude that the **** network is broken. This is a general issue for any network where configurations for MC forwarding is needed and where initial igmp reports may get lost. A staggering of time intervals would be a general solution to that issue. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html