Hi, I have a media server (Flussonic) installed on Debian 12.9 that is subscribed to hundreds of IGMP groups and, when the querier sends a "general query", the media server answers back with a oversized "Joint group" paquet larger than the interface MTU and drops in egress.
By exemple, with default 1500 MTU, from a capture, I can see a first "Joint group" paquet with a size of 1506 that won't hit my switch and a second smaller paquet sent with the remaining groups that will reach my switch. The size of the paquet seems to be based on interface MTU because if I change the MTU to a larger value, I now see a single larger "Joint group" paquet sent. But it would mean changing the MTU on the whole network and if I subscribe to more groups, I presume I will eventually oversize the new MTU again. I contacted Flussonic and they told me they can do nothing, that they only make calls through the OS API socket and that the IGMP subscriptions are handled by the kernel. So, I wonder if there is a way to limit the "Joint group" so it won't go over the interface MTU ? I didn't see any IGMP option that seems related in sysctl. Thanks
