TL-SG1005LP appears to block/consume IGMPv2 packets
TL-SG1005LP appears to block/consume IGMPv2 packets
Hi,
I'm developing a consumer device based on a ST micro with lwIP as the TCP/IP stack. One requirement - based on interoperation with existing products - is to respond to multicast UDP packets that are used as a form of device discovery. To make routers forward the UDP packets I need to use IGMP to join the relevant group. This is trivial and seems to work well. The lwIP stack uses IGMPv2.
The problems start when I connect my board to an unmanaged TP-Link switch (TL-SG1005LP) in my office and access the network that way. I've used Wireshark to monitor the traffic during the 'join group' phase and have observed as below:-
- When the device and PC are connected directly through the main router, the IGMPv2 messages appear on Wireshark and multicast packets are received at the device.
- When the device is connected through the switch, the IGMPv2 packets are not seen in Wireshark and multicast packets are not received.
The only conclusion I can draw is that the switch is either filtering or consuming the IGMPv2 packets.
I have other devices that use the same mechanism but with IGMPv3 packets - interestingly these always get through.
Questions:-
- Is this expected behaviour or a bug? If expected - why? If a bug - is there a fix?
- As the switch is unmanaged, can I configure it to not drop these packets?
- Is this the same across other TP-Link devices?
- Do other manufacturers' switches have this issue? What switch do I need that will not do this?
Thanks for any assistance.
Chris
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Hi @CShaw
Thanks for posting in our business forum.
CShaw wrote
@Clive_A Thanks for continuing to look into this, your help is much appreciated.
The PC is in the mutlicast group - I have used the `socat` utility to ensure it is joined. I have disabled IGMP snooping on the wireless router and this is why the IGMPv2 packets are seen in the first instance.
It would be helpful if you were able to try and reproduce this, but I understand this may not be possible. I can't really 'try out' different models without purchasing, so this isn't really possible.
I'll weigh up whether to buy a SG2210MP instead - if this may work - or to get a Cisco unit.
Regards,
Chris
Can you show me the screenshot of your "socat" utility which indicates the PC has joined the multicast group where Wireshark did not show anything about IGMPv2 joining?
Is the Wireshark result the same as the previous screenshot you gave me?
I need this information to discuss with the test team to finally determine if we need to do something else. I would require more details about this. Or maybe I should get the test team to remote your computer to check this out.
To replicate what you suggested might be hard for us. We don't have the gears you have. If you simply want to test the IGMPv2, we have not found anything buggy and no known issue was listed internally.
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@Clive_A The info you requested is visible in the previous Wireshark capture. In this setup:-
- The PC is address 192.168.0.115
- There is a VM on the PC at address 192.168.0.117
You can see IGMPv3 messages from both these devices in both screenshots where they join the 239.192.0.1 multicast group.
The dev device is at 192.168.0.106 which is only able to join the group via IGMPv2 in the first capture when NOT behind the switch.
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@Clive_A Thanks for the continued support.
FYI I have just purchased and tested the same setup with a SG2210MP and this behaves correctly straight out of the box; the IGMPv2 Join Group message is propagated around the network and the appropriate multicast traffic is then correctly delivered to my device.
I'm going to move on with my work rather than spend any more time trying to use the SG1005, but I maintain that this is blocking the IGMPv2 traffic and therefore not working correctly.
Thanks and regards,
Chris
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