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?
Andrew
