netdev - Re: IGMP snooping: set mrouters_only flag for IPv4 traffic properly

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Date:	Tue, 14 Jun 2011 13:22:12 -0400
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, netdev@...r.kernel.org,
	Hayato Kakuta <kakuta.hayato@....ntt.co.jp>
Subject: Re: IGMP snooping: set mrouters_only flag for IPv4 traffic properly

On Mon, 13 Jun 2011 12:02:43 +0900
Fernando Luis Vazquez Cao <fernando@....ntt.co.jp> wrote:

> Upon reception of a IGMP/IGMPv2 membership report the kernel sets the
> mrouters_only flag in a skb that may be a clone of the original skb, which
> means that sometimes the bridge loses track of membership report packets (cb
> buffers are tied to a specifici skb and not shared) and it ends up forwading
> join requests to the bridge interface.
> 
> This can cause unexpected membership timeouts and intermitent/permanent loss of connectivity as described in RFC 4541 [2.1.1. IGMP Forwarding Rules]:
> 
>     A snooping switch should forward IGMP Membership Reports only to
>     those ports where multicast routers are attached.
>     [...]
>     Sending membership reports to other hosts can result, for IGMPv1
>     and IGMPv2, in unintentionally preventing a host from joining a
>     specific multicast group.
> 
> 
> Signed-off-by: Fernando Luis Vazquez Cao <fernando@....ntt.co.jp>
> Tested-by: Hayato Kakuta <kakuta.hayato@....ntt.co.jp>
> ---
> 
> diff -urNp linux-3.0-rc2-orig/net/bridge/br_multicast.c linux-3.0-rc2/net/bridge/br_multicast.c
> --- linux-3.0-rc2-orig/net/bridge/br_multicast.c	2011-06-09 13:34:04.164261031 +0900
> +++ linux-3.0-rc2/net/bridge/br_multicast.c	2011-06-09 20:04:23.473930447 +0900
> @@ -1424,7 +1424,7 @@ static int br_multicast_ipv4_rcv(struct
>  	switch (ih->type) {
>  	case IGMP_HOST_MEMBERSHIP_REPORT:
>  	case IGMPV2_HOST_MEMBERSHIP_REPORT:
> -		BR_INPUT_SKB_CB(skb2)->mrouters_only = 1;
> +		BR_INPUT_SKB_CB(skb)->mrouters_only = 1;
>  		err = br_ip4_multicast_add_group(br, port, ih->group);
>  		break;
>  	case IGMPV3_HOST_MEMBERSHIP_REPORT:

Acked-by: Stephen Hemminger <shemminger@...tta.com>
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