Find printers and speakers across VLANs#

You will end up with discovery announcements repeated between two or more networks, so a phone on the client VLAN can find a printer on the infrastructure VLAN. Chromecasts, AirPlay speakers, network printers and most devices that "just appear" rely on mDNS, and mDNS does not cross a router.

Before you start#

The operator role and a licence.
At least two interfaces with addresses. The repeater needs somewhere to repeat between.
A decision about what this costs, below.

Step 1 — Turn on the repeater#

Services → DNS, mDNS tab, Turn on the mDNS repeater.

Tick the interfaces to repeat between — the LAN and the VLAN, say. VLANs are listed like any other interface.
Choose the Address family. Every ticked interface needs an address of each family repeated; the form names one that has none. IPv4 only is the usual choice on a network without IPv6.
Under Services, list only what needs to cross — _ipp._tcp for printers, _airplay._tcp and _raop._tcp for AirPlay, _googlecast._tcp for casting — or leave it empty to repeat everything.
Save changes, and apply.

Step 2 — Let the discovered thing be reachable#

Discovery and access are separate. A phone that can now see the printer still needs a firewall rule to reach it: allow the client network to the printer's address and port, and nothing wider — see a default-drop ruleset. Scoping the rule to one address is the difference between "guests can print" and "guests are on the infrastructure VLAN".

Check it worked#

From a client on the far network:

bash

avahi-browse -at
dns-sd -B _services._dns-sd._udp

The device should appear. If it appears and does not work, that is the firewall rule, not the repeater.

When it does not help#

Not every "it just appears" protocol is mDNS. SSDP, WS-Discovery and several vendors' own discovery are other protocols, and this repeater does not carry them. If the device is still not found and avahi-browse shows nothing, it probably does not use mDNS — give the client the device's address directly.

Undoing it#

Edit → Remove on the mDNS tab, or Disabled to keep the settings and stop repeating.