Wireless Multicast Forwarding on OpenWRT

igorv asked:

Good day!

We need to connect an STB device over wi-fi to the router. STB uses multicast only. Using udpxy is not possible. Original firmware forwards multicast over wi-fi using mac changing technique. I.e. router changes destination mac address from multicast to unicast mac address of multicast group subscriber. On Asus routers this feature is called “Wireless Multicast Forwarding (WMF)”. On Mikrotik it’s called “Multicast-helper”. So, the question is: Can I enable this on TP-link wr741nd with ŠžpenWrt? It works in original firmware. How is it implemented? Is it a feature of wi-fi chip driver or kernel patch or patch of igmpproxy or something else?

My answer:

The OpenWrt wiki had an answer:

With IGMP snooping, multicast forwarding is disabled for bridges. One
pure bridge solution is to disable multicast_snooping.

Add the following in /etc/rc.local

echo "0" > /sys/devices/virtual/net/br-lan/bridge/multicast_snooping

Replace br-lan with your actual bridge interface, sometimes also
called br0.

This will forward all multicast packets to all ports on your bridge,
making igmpproxy or udpxy unnecessary. In large networks, this may not
be desirable.

Also remember that multicast over Wi-Fi is a performance killer.

View the full question and answer on Server Fault.

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