Starting with VyOS 1.2 a mDNS repeater functionality is provided. Additional information can be obtained from https://en.wikipedia.org/wiki/Multicast_DNS.
Multicast DNS uses the 220.127.116.11 address, which is “administratively scoped” and does not leave the subnet. It retransmits mDNS packets from one interface to other interfaces. This enables support for e.g. Apple Airplay devices across multiple VLANs.
Since the mDNS protocol sends the AA records in the packet itself, the repeater does not need to forge the source address. Instead, the source address is of the interface that repeats the packet.
You can not run this in a VRRP setup, if multiple mDNS repeaters are launched in a subnet you will experience the mDNS packet storm death!
To listen on both eth0 and eth1 mDNS packets and also repeat packets received on eth0 to eth1 (and vice-versa) use the following commands:
set service mdns repeater interface 'eth0' set service mdns repeater interface 'eth1'