netdev - Re: IGMP v3 reponse

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Date:	Mon, 27 Sep 2010 17:41:57 -0700
From:	David Stevens <dlstevens@...ibm.com>
To:	Bob Arendt <rda@...con.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>
Subject: Re: IGMP v3 reponse

Bob Arendt <rda@...con.com> wrote on 09/27/2010 04:51:15 PM:

> Per rfc 2236, the v2 client *can't* drop the IGMPv3 query.  From para 
2.5:
>    2.5.  Other fields
>     Note that IGMP messages may be longer than 8 octets, especially
>     future backwards-compatible versions of IGMP.  As long as the Type 
is
>     one that is recognized, an IGMPv2 implementation MUST ignore 
anything
>     past the first 8 octets while processing the packet.  However, the
>     IGMP checksum is always computed over the whole IP payload, not just
>     over the first 8 octets.
> 
> The IGMPv3 query *is* a valid v2 query with extra crap at the end (it's
> backward compatible).  Per rfc 2236 p2.5, the v3 query has to be 
regarded
> as a valid v2 query if you're correctly implementing IGMPv2.  Some 
switch
> vendors (Cisco for one) only generate v3 queries when operating as an
> IGMP snooping switch, since a proper v2 client will respond with IGMPv2
> packets and it handles this properly.  However, we're seeing some 
switches
> get confused when a client initial joins with v2, then responds to a 
query
> with v3.  It ends up creating 2 entries, and only one is cleared by the
> leave message.  This is also an issue when the primary (querier) switch
> only generates v3 queries, and some intermediate switches only support 
v2.
> We set all the Linux clients to v2 .. but they respond the v2 query with
> v3 protocols, which could be missed by the intermediate switch.
> 
> I believe the intent of the bug 18212 patch is correct.

Bob,
        That would've been a nice quote for the other discussion; I didn't
do the v2 implementation for Linux, but it appears I broke this. I'll
take another look (and thanks for pointing that out!).

                                                        +-DLS

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