@Fae
Thank you for your reply.
In fact I have home automation system behind the switch which is connecter to my internet router.
And I have wifi network directly on the router with google devices.
it requires mdns to work between my automation server and the google devices
My option would be to get a larger switch and move the wifi network behind the same switch. But even here i'm not sure mdns would work internally in the same LAN.
And and I have not idea if having a lot of devices wifi/wired behind the switch and linked just with one RJ45 to the router is a good idea.
that's why my current wish is to enable mdns...
A