Why is IGMP Snooping in br-lan always problematic?

Installing and Using OpenWrt
1

I always enable IGMP Snooping in br-lan but whenever something starts using multicast I have problems and I need to disable it.

Years ago I used to use DLNA and if I enabled IGMP Snooping in br-lan the DLNA clients connected by wireless shortly after starting playback would stop working.

Now my ISP offers native IPv6 so I configure it and when I start testing it, it works perfectly on the devices connected to the router by wireless but on the devices connected by wired it doesn't work. Again IGMP Snooping giving problems, it breaks DHCPv6 (IPv6 fail on wired network and work on wireless network).

To activate it I simply add option igmp_snooping '1' in “/etc/config/network”:

config device
	option name 'br-lan'
	option type 'bridge'
	option igmp_snooping '1'
	list ports 'lan0'
	list ports 'lan1'
	list ports 'lan2'
	list ports 'lan3'
	list ports 'lan4'

Am I doing something wrong or does OpenWRT have a problem with IGMP or is this a common Linux problem?

2

Nope, your stream clients have to refresh group membership in igmp2 network every 125s, which ancient igmp1 clients will not do.
tcpdump and wireshark are your friends

3

I will try to get time to test with tcpdump and try to understand the capture with wireshark.

But after looking for more information I think it may be a problem specific to my device (Turris Omnia) and its DTS / DTB:

And the symptoms seem to fit with the ones I had using IGM Snooping with DHCPv6 (IPv6 fail on wired network and work on wireless network):

4

I have no way to confirm that but I had issues with Wireshark and multicast.
As soon as I started Wireshark, the multicast traffic stopped. I had seen it with ospf. But could be unrelated... Maybe start it one time with promisc mode and one time without to rule out capture issues.

5

You can use -p/-P to control settong interface to promiscuous mode.