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GS752TPv2 Multicast: initial IGMP Membership Report gets lost
We are developing an application on a small STM32 microcontroller that connects to the network, using lwIP tcp/ip stack. Our application subscribes to a Multicast address. When we use any other switch, we can see that our device sends a IGMP membership report everytime we connect it to the switch (two on the very first connection, as defined by the IGMPv2 standard), and then it responds to IGMP Queries correctly. We analyze all of this with Wireshark. Therefore, if we enable IGMP Snooping on the switch, it works: our device is subscribed to the required multicast address as soon as we connect it, and we receive all packets.
When we connect our device to the GS752TPv2 switch, something changes: we can see that it responds to IGMP Queries correctly, but the IGMP membership reports sent on initial connections are dropped by the switch. This seems to happen because our device has a very short boot time (there is no operating system), so it seems that the switch is not ready to receive packets so fast. If we enable IGMP Snooping of the switch, it doesn't work at first, because the initial IGMP Membership Report is lost, so the switch doesn't add the device's port to the IGMP Snooping Table. It only starts working correctly after the IGMP Querier sends a Query and our device responds. This delay, which can be as long as the IGMP Query Interval, is unacceptable to us.
We have tried to force our device to wait some seconds after booting, before subscribing to the Multicast address: if we do that, it works, because the switch doesn't drop the IGMP membership report. But this initial delay is not acceptable to us.
In the switch configuration, we have also observed, under Monitoring->Port Detailed Statistics, that everytime we connect our device, the "Total Received Packets Not Forwarded" and "Dropped Transmit Frames" parameters get incremented by 5, which makes us think that the IGMP Membership Reports that our device is sending are among those dropped frames, but we don't have any more information.
