I was able to work around the problem by lowering the server NIC MTU to 1480. The report paquet is now under 1500 (1494). Since the video segments also have a length under 1500, it works fine in my case.
Le mer. 19 févr. 2025 à 09:23, Michel Blais <michel.blais...@gmail.com> a écrit : > 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 > > -- Cordialement, / With regards, Michel Blais
