From: Dongpo Li <lidongpo@hisilicon.com>
To: Andrew Lunn <andrew@lunn.ch>
Cc: netdev <netdev@vger.kernel.org>
Subject: Re: question about function igmp_stop_timer() in net/ipv4/igmp.c
Date: Tue, 25 Oct 2016 09:13:54 +0800 [thread overview]
Message-ID: <580EB1D2.3010309@hisilicon.com> (raw)
In-Reply-To: <20161024153200.GM1110@lunn.ch>
Hi Andrew,
On 2016/10/24 23:32, Andrew Lunn wrote:
> On Mon, Oct 24, 2016 at 07:50:12PM +0800, Dongpo Li wrote:
>> Hello
>>
>> We encountered a multicast problem when two set-top box(STB) join the same multicast group and leave.
>> The two boxes can join the same multicast group
>> but only one box can send the IGMP leave group message when leave,
>> the other box does not send the IGMP leave message.
>> Our boxes use the IGMP version 2.
>>
>> I added some debug info and found the whole procedure is like this:
>> (1) Box A joins the multicast group 225.1.101.145 and send the IGMP v2 membership report(join group).
>> (2) Box B joins the same multicast group 225.1.101.145 and also send the IGMP v2 membership report(join group).
>> (3) Box A receives the IGMP membership report from Box B and kernel calls igmp_heard_report().
>> This function will call igmp_stop_timer(im).
>> In function igmp_stop_timer(im), it tries to delete IGMP timer and does the following:
>> im->tm_running = 0;
>> im->reporter = 0;
>> (4) Box A leaves the multicast group 225.1.101.145 and kernel calls
>> ip_mc_leave_group -> ip_mc_dec_group -> igmp_group_dropped.
>> But in function igmp_group_dropped(), the im->reporter is 0, so the kernel does not send the IGMP leave message.
>
> RFC 2236 says:
>
> 2. Introduction
>
> The Internet Group Management Protocol (IGMP) is used by IP hosts to
> report their multicast group memberships to any immediately-
> neighboring multicast routers.
>
> Are Box A or B multicast routers?
Thank you for your comments.
Both Box A and B are IP hosts, not multicast routers.
And the RFC says: IGMP is used by "IP hosts" to report their multicast group membership.
>
> Andrew
>
> .
>
Regards,
Dongpo
.
next prev parent reply other threads:[~2016-10-25 1:16 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-24 11:50 question about function igmp_stop_timer() in net/ipv4/igmp.c Dongpo Li
2016-10-24 15:32 ` Andrew Lunn
2016-10-25 1:13 ` Dongpo Li [this message]
2016-10-25 7:39 ` Andrew Lunn
2016-10-25 11:50 ` Dongpo Li
2016-10-25 12:19 ` Andrew Lunn
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