On 15/11/2020 17:27, Andrew Lunn wrote: > So check if you have an IGMP querier in the network. If not, try > turning it on in the bridge, > > ip link set br0 type bridge mcast_querier Thankfully it turns out this is totally unrelated to Linux - our TP-Link Jetstream T1600G-PS has some unfortunate default behaviour and a bug.
Specifically, we are operating an IPv6-only network and Layer 2 MLD snooping was enabled and set to forward unknown multicast groups and as such the switch should be broadcasting all multicast packets. However, buried in the TP-Link manual there's a note that says: "Note: IGMP Snooping and MLD Snooping share the setting of Unknown Multicast Groups, so you have to enable IGMP Snooping globally on the L2 FEATURES > Multicast > IGMP Snooping > Global Config page at the same time." We hadn't enabled IGMP snooping since we don't use IPv4! Many thanks for the help resolving this and apologies for mis-reporting it.
