Enable Multicast between WIFI devices

#1

I want to set up the system where Xiaomi MiHome Bridge reads the information from the temperature sensors and sends it to OpenHAB installed on a win10 PC. I use NETGEAR EX3700 (with OpenWRT r9992) in AP mode to provide a wifi network, where the communication between the MiHome Bridge and the PC occurs.

It's working fine (OpenHAB can connect to the Bridge and read the sensors info) with one exception: MiHome Bridge is supposed to send short heartbeat signals using multicast every few seconds. I'm checking with WireShark on the PC whether these signals are sent, and I see none. The result is that within some minutes after initial connection OpenHAB thinks that MiHome bridge has gone offline.

As I understand, that's because OpenWRT disables multicast traffic over WiFi by default. I'm new to OpenWRT and I don't know how to properly enable it. Of course I have seen IPTV/UDP multicast page, but that's mostly about routing WAN multicast traffic to WiFi devices, whereas I just need to enable multicast within WLAN. There's an example of using route add -net 224.0.0.0 ... command, which may help, but I don't know how to translate it into /etc/config/network or LuCI setup.