pkg-descr

udbproadcastrelay is a USB multicast relayer. Its intended use is to
rebroadbcast udp packets on a specific port across interfaces, be those
interfaces physical or VLAN. 

It is used where devices such as Sonos or Sky are spread accross 
different subnets and are not able to detect the servers or devices.

Examples of different devices and the ports are as follows:

Syncthing discovery 
udp_vars="--id 1 --port 21027 --dev igb1 --dev igb2"

mDNS / Broadcast DNS (Chromecast Discovery + Bonjour + More)
udp_vars="--id 1 --port 5353 --dev eth0 --dev eth1 --multicast 224.0.0.251 -s 1.1.1.1"

(Chromecast requires broadcasts to originate from an address on its subnet) use
the rebroadbcast address option.

SSDP (Sonos Roku Discovery + More)
udp_vars="--id 1 --port 1900 --dev eth0 --dev eth1 --multicast 239.255.255.250"

Lifx Bulb Discovery
udp_vars=" --id 1 --port 56700 --dev eth0 --dev eth1"

Broadlink IR Emitter Discovery
udp_vars=" --id 1 --port 80 --dev eth0 --dev eth1"

Warcraft 3 Server Discovery
udp_vars=" --id 1 --port 6112 --dev eth0 --dev eth1"