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
.
