GL-B1300 (v3.211) multicast


I have a gl-b1300 running v3.211 and I enabled multicast (admin panel → applications → igmp snooping → enable). Multicast data appears to be going to all devices on the network, not just devices listening to the multicast address.

Physical setup is, gl-b1300 wired to tplink sg108 (v1.3) which has three machines wired to it.
machine1 runs: gst-launch-1.0 videotestsrc ! x264enc ! rtph264pay ! udpsink host= port=20000 auto-multicast=true
machine2 runs: gst-launch-1.0 udpsrc address= port=20000 auto-multicast=true ! application/x-rtp, encoding-name=H264, payload=96 ! rtph264depay ! decodebin ! videoconvert ! autovideosink
machine3 runs: sudo tcpdump -i eth0 port 20000

machine1 and 2 run as expected, sending and receiving data. However machine3 also receives the data,

16:32:28.781045 IP jetson.lan.52343 > UDP, length 1400
16:32:28.781118 IP jetson.lan.52343 > UDP, length 1400

I thought the data would be filtered and only sent to requesting machines. Is this incorrect?



That’s right, igmp snooping: Layer 2 devices maintain and manage Layer 2 multicast forwarding tables by listening to IGMP packets, and transparently transmit all IGMP packets between routers and multicast members