Multicast across subnets

Networking & Firewalls
3

There are two different protocols in use for domesic AV equipment and you need different services to make those work acress routed networks:

  • mDNS (used e.g. by Apple AirPlay) → udp broadcast relay, or AVAHI (don’t use both!)
  • SSDP (used by DLNA/UPnP) → udp broadcast relay

I don’t know what Google is using, possibly Chromecast, and I dont know anything about Chromecast, but googling shows it may use SSDP.

Your best guess is UDP Broadcast Relay (additional package to install using the package manager):