netdev - Re: IGMP Unsolicited Report Interval too long for IGMPv3?

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Message-Id: <20130725.164253.690113010547536005.davem@davemloft.net>
Date:	Thu, 25 Jul 2013 16:42:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hannes@...essinduktion.org
Cc:	bcrl@...ck.org, william.manley@...view.com, netdev@...r.kernel.org
Subject: Re: IGMP Unsolicited Report Interval too long for IGMPv3?

From: Hannes Frederic Sowa <hannes@...essinduktion.org>
Date: Mon, 22 Jul 2013 23:51:08 +0200

> On Mon, Jul 22, 2013 at 05:18:55PM -0400, Benjamin LaHaise wrote:
>> On Mon, Jul 22, 2013 at 09:43:57PM +0100, William Manley wrote:
>> > If an IGMP join packet is lost you will not receive data sent to the 
>> > multicast group so if no data arrives from that multicast group in a 
>> > period of time after the IGMP join a second IGMP join will be sent.  The 
>> > delay between joins is the "IGMP Unsolicited Report Interval".
>> > 
>> > In the kernel this seems to be hard coded to be chosen randomly between 
>> > 0-10s.  In our use-case (IPTV) this is too long as it can cause channel 
>> > change to be slow in the presence of packet loss.
>> > 
>> > I would guess that this 10s has come from IGMPv2 RFC2236, which was 
>> > reduced to 1s in IGMPv3 RFC3376.
>> 
>> Reducing the timeout does not solve the problem you are encountering, as 
>> any packet loss will still result in a 1 second delay.  I've encountered 
>> similar issues dealing with LCP Echo request/replies for keepalive 
>> messages on PPP sessions.  The correct approach is to queue the IGMP 
>> multicast join with a higher priority than other traffic in the system 
>> so that the requests are not lost due to congestion of a single queue.  
>> Sending packets with an 802.1p header might be appropriate in your 
>> use-case, or perhaps using higher priority internal queues.
> 
> Yes, we can do a little bit better. What do you think?
> 
> [PATCH net-next] ipv6: send igmpv3/mld packets with TC_PRIO_CONTROL
> 
> Reported-by: William Manley <william.manley@...view.com>
> Suggested-by: Benjamin LaHaise <bcrl@...ck.org>
> Signed-off-by: Hannes Frederic Sowa <hannes@...essinduktion.org>

Ben, please give Hannes the feedback he is asking for.

Thanks.
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