So mobile operating systems are strange and limited beasts. Android doesn’t allow us to enable Multicast on the interface they give us directly. Before Android 10 was released, we could poll /proc/net/igmp to determine what multicast groups that ZeroTier should listen to, and things were good.
Android 10 was released and it included a lot of privacy updates, and we lost access to everything under /proc/net/. As such, we can no longer automatically listen to multicast groups that are listened to in other applications. The one workaround is the one you discovered. If you send a multicast packet over the ZeroTier network, the multicast emulation in ZeroTier will automatically start listening on that group as well.
Thank you very much for the quick reply.
Then we will keep this life hack with empty multicast packet.
It is not a very big issue and it works pretty well.