I have a setup in which one Raspberry Pi 3 is publishing ethernet multicast traffic and another Raspberry Pi acting as a subscriber. Both are on a wired connection, plugged into the same switch and are on the same subnet. I noticed by running tcpdump on the subscriber pi that it was completely oblivious to any multicast traffic and was not producing any output at all. I then plugged in an Ubuntu VM into the same switch and running wireshark, was able to see the multicast traffic. I have tried enabling promiscuous mode on interface eth0 of the subscriber Pi but still am unable to see the multicast traffic that the Ubuntu VM is somehow able to see. Are there any configurations that need to be changed so I can see this traffic on the Pi?

  • What does it mean "one Raspberry Pi 3 is publishing ethernet multicast traffic"? Is it a multicast server sending igmp queries? Does the switch supports multicasting and has igmp snooping enabled or is it a dumb one that simply broadcasts multicast packages to all ports? When testing with the Ubuntu machine do you pull out the subscribers ethernet cord from the switch and plug in the cord from the Ubuntu machine into the same port? – Ingo Dec 14 '18 at 19:38
  • The Pi is sending Sampled Values traffic (Ethtype 0x88BA), no IGMP involved and it is my belief that it should be spamming out all ports as I was able to see it in the VM. When testing with the Ubuntu machine, I just plug it into the same switch that the RPis were on without disconnecting anything else. – dapirateking Dec 14 '18 at 22:18
  • Never heard about this before but with a quick view at google - Sampled Values traffic it seems to be very abstract and academic and mostly used for communication in smart grids - interesting. But Traffic sampling enables you to copy traffic to a Physical Interface Card (PIC) that performs flow accounting while the router forwards the packet to its original destination. - huu?? Do you believe Raspberry Pi can do that? – Ingo Dec 14 '18 at 23:31
  • I'm not too sure if the Raspberry Pi can do what you had mentioned but I am not doing anything with routers and also I know that the Pi is emitting multicast traffic as I am able to view it in at least one VM connected to the network. – dapirateking Dec 17 '18 at 17:03

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