We are using the latest Thread stack version, with a KW21D512 used as a host-controlled device, set up to use a serial FSCI connection to an iMX6UL.
The HCD has been setup as a serial TUN device.
While sending normal unicast request works well, we found out that sending out requests to multicast address doesn't work.
We do it the following way: we send a CoAP GET request to a custom multicast address (which our device subscribe to) `coap://[FF03::ABBE:55E5]/m/version`.
The python VTUN interface shows the packet arriving, and forwards it to the radio. We have the `TX: 6000000000191101fd010000000000000000000000000002ff0300000000000000000000abbe55e582e21633001983a6480159225720e7c960ed8c82b16d026964`.
Except then, nothing happens over the air. The packet never shows up.
I believe this could be a simple setup problem, or a configuration in the HCD software.
Any hints or leads to solve that?