netdev - Re: [PATCH v4 1/3] net: igmp: Reduce Unsolicited report interval to 1s when using IGMPv3

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Date:	Wed, 7 Aug 2013 02:45:23 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	William Manley <william.manley@...view.com>
Cc:	netdev@...r.kernel.org, bcrl@...ck.org, luky-37@...mail.com,
	sergei.shtylyov@...entembedded.com, bhutchings@...arflare.com,
	davem@...emloft.net
Subject: Re: [PATCH v4 1/3] net: igmp: Reduce Unsolicited report interval to 1s when using IGMPv3

On Tue, Aug 06, 2013 at 07:03:13PM +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".
> 
> Previously this value was hard coded to be chosen randomly between 0-10s.
> This can be too long for some use-cases, such as IPTV as it can cause
> channel change to be slow in the presence of packet loss.
> 
> The value 10s has come from IGMPv2 RFC2236, which was reduced to 1s in
> IGMPv3 RFC3376.  This patch makes the kernel use the 1s value from the
> later RFC if we are operating in IGMPv3 mode.  IGMPv2 behaviour is
> unaffected.
> 
> Tested with Wireshark and a simple program to join a (non-existent)
> multicast group.  The distribution of timings for the second join differ
> based upon setting /proc/sys/net/ipv4/conf/eth0/force_igmp_version.
> 
> Signed-off-by: William Manley <william.manley@...view.com>

Acked-by: Hannes Frederic Sowa <hannes@...essinduktion.org>
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