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

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Message-ID: <OF871D4733.876C9DA0-ON882577AB.006AB200-882577AB.006B6101@us.ibm.com>
Date:	Mon, 27 Sep 2010 12:32:45 -0700
From:	David Stevens <dlstevens@...ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	linux-rdma@...r.kernel.org, netdev@...r.kernel.org,
	Bob Arendt <rda@...con.com>
Subject: Re: igmp: Staggered igmp report intervals for unsolicited igmp reports

Christoph Lameter <cl@...ux.com> wrote on 09/23/2010 10:37:28 AM:

> 
> 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.

        You can, of course, add a querier (or configure it, assuming
an attached switch supports it) and set the query interval and robustness
count as appropriate for that network.

> This is a general issue for any network where configurations for MC
> forwarding is needed and where initial igmp reports may get lost.

Meaning "IB-only", right? :-) Maybe other NBMA networks too, but
certainly not a typical problem for typical networks (i.e., Ethernet).

> A staggering of time intervals would be a general solution to that 
issue.

As would be having those networks queue packets for hardware addresses 
they
know require a delay before a transmit can complete. But that approach 
can't
adversely affect already-working solutions for typical networks, or
depart unnecessarily from established standard protocols.

 +-DLS

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