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

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Message-ID: <20130726131123.GC1281@kvack.org>
Date:	Fri, 26 Jul 2013 09:11:23 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	David Miller <davem@...emloft.net>
Cc:	hannes@...essinduktion.org, william.manley@...view.com,
	netdev@...r.kernel.org
Subject: Re: IGMP Unsolicited Report Interval too long for IGMPv3?

On Thu, Jul 25, 2013 at 04:42:53PM -0700, David Miller wrote:
> 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.

I think Hannes' patch is good step in the right direction, so please add:
Acked-by: Benjamin LaHaise <bcrl@...ck.org>

		-ben
-- 
"Thought is the essence of where you are now."
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