It took nearly a year for me to land on this simple solution, and it was found coincidentally by me trying to enable cross-subnet AirPlay (sorry, still haven’t gotten that to work securely).
Enable cross-subnet Chromecast casting
To enable casting via Chromecast between subnets, simply do the following.
- New Unifi UI: Settings > Gateway > MDNS > Enable Multicast DNS
- Old Unifi UI: Settings > Services > MDNS > Enable Multicast DNS
Now from any USG network interface, you will be able to reach our Chromecast devices for casting.
What is mDNS reflector?
The reflector does as the name suggests: It will relay/repeat any Multicast traffic from the interface it was initiated on, to the interfaces you have configured on your USG.