Multicast IGMP reports missing

Software SW help
1

Hi,

I’m running 6.0.2 on my Omnia.

I’ve got a device wired directly to lan4, which is configured as:

config interface 'VERO'
	option proto 'static'
	option ipaddr '192.168.2.1'
	option netmask '255.255.255.0'
	option ip6assign '64'
	option ip6hint '2'
	option device 'lan4'

This device in question has IPv4 address 192.168.2.21. In that device, if I try to join multicast group 239.77.3.6 via:

socat STDIO UDP4-DATAGRAM:239.77.3.6:8889,ip-add-membership=239.77.3.6:192.168.2.21

I can see on the device via tcpdump (with tcpdump -i eth0 -vv src 192.168.2.21 and igmp -n) the IGMPv2 report packets to join the group:

09:22:21.516913 IP (tos 0xc0, ttl 1, id 0, offset 0, flags [DF], proto IGMP (2), length 32, options (RA))
    192.168.2.21 > 239.77.3.6: igmp v2 report 239.77.3.6

However if I listen on the Omnia side with tcpdump -i lan4 -vv src 192.168.2.21 and igmp -n I cannot see any traffic at all. Other traffic like ICMP or TCP is visible as it should.

Does anybody know why?

Thanks.

2

Afaik tcpdump is case-sensitive, try filtering with IGMP

3

Thanks for your suggestion.

I think the filter is okay, it works fine in the “client” (the device with IPv4 address 192.168.2.21 wired to lan4) and the versions of tcpdump and libpcap are very similar. Anyway, I gave it a go:

~ # tcpdump -i lan4 -vv src 192.168.2.21 and IGMP -n
tcpdump: unknown host 'IGMP'
4

So far everything points to the interface in the router or the driver (DSA?) dropping the traffic. I’m not alone, though.

5

Maybe try by temporarily disabling firewall service and see if the firewall is the culprit

6

Thanks. libpcap sees inbound traffic before it’s processed by netfilter so it shouldn’t be a firewall issue. It looks like the traffic is dropped by the NIC or the driver.

7

I can confirm the same problem. I just spent quite a while trying to figure this out and so far without success.

Turris OS version 6.2.4
Kernel version 5.15.94

One thing that I noticed and that may help pinpoint it is that there is some inbound multicast traffic visible on the bridge interface of the router from devices connected via wifi - a laptop and some android phones. But with two desktop machines that are connected over wired connection, no dice.

It appears that something happened with the way the physical ports/switch are configured, or a ethernet device driver or something. One thing that I’m going to try out when I get a bit of time is whether the one extra ethernet port that is connected directly to the CPU instead of over the switch behaves differently. That could help it pinpoint further.

8

I just tried to switch the ports a bit and it appears that it doesn’t matter whether I connect the machine to LAN3 or LAN4 ports.

9

@fissie yep, I got to the same conclusion, see: Multicast IGMP reports missing - #7 by avioneta - Installing and Using OpenWrt - OpenWrt Forum