Find printers and speakers across VLANs#

You will end up with multicast discovery announcements repeated between two or more segments, so a phone on the client VLAN can find a printer on the infrastructure VLAN. Chromecasts, AirPlay speakers, network printers and most "it just appears" devices 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 — Configure the repeater#

Network → DNS → mDNS.

set service mdns repeater interface eth0
set service mdns repeater interface eth0.30
set service mdns repeater ip-version 4

One interface line per segment. At least two are required — the page will not let you remove an interface when only two remain, because a repeater with one interface repeats nothing.

ip-version restricts it to one family; leave it unset to repeat both.

Step 2 — Let the discovered thing be reachable#

Discovery and access are separate. A phone that can now see the printer still needs a forward rule to reach it.

set firewall ipv4 forward filter rule 60 action accept
set firewall ipv4 forward filter rule 60 description 'guests to the printer'
set firewall ipv4 forward filter rule 60 inbound-interface name eth0.30
set firewall ipv4 forward filter rule 60 destination address 192.0.2.10

Scoping the rule to one address is the difference between "guests can print" and "guests are on the infrastructure VLAN". A default-drop ruleset.

Check it worked#

From a client on the far segment:

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.

On the router:

bash

show configuration commands | match mdns

When it does not help#

Not every "it just appears" protocol is mDNS. SSDP, WS-Discovery and several vendors' own discovery mechanisms are different protocols, and this repeater does not carry them. If the device is not found after the repeater is up and avahi-browse shows nothing, it is probably not using mDNS at all — and the answer is usually to give the client the device's address directly.

Undoing it#

delete service mdns

The page's Remove repeater stages exactly that.