mDNS repeater#
The fourth tab of DNS, at /dns.
Printers, speakers and casting devices announce themselves with multicast DNS, which stays on its own network: it does not cross a router. Put the televisions on an IoT VLAN and the laptops on the LAN and they stop seeing each other. The repeater repeats those announcements between the networks you choose, and discovery works across them again.
The repeater#
When it is on, the panel lists:
| Field | What it shows |
|---|---|
| Repeats between | the interfaces |
| Address family | IPv4 and IPv6, or one of them |
| Services | the service types repeated, or All |
| Extra browsing domains | domains announced beyond the default one |
| Cache | entries kept per interface |
| State | On, Off, or on only while this router is the VRRP master |
When it is off, Turn on the mDNS repeater opens the form. Edit opens the same form for a repeater that exists.
The form#
| Field | What it does |
|---|---|
| Repeat between | a checkbox for every interface, VLANs included; at least two |
| Address family | IPv4 and IPv6, IPv4 only or IPv6 only |
| Services | the service types to repeat, such as _airplay._tcp; empty repeats every one |
| Extra browsing domains | domains to announce besides the default one |
| Cache | entries kept per interface, 4096 when unset |
| Only while this router is the VRRP master | on a VRRP pair, stops the backup repeating |
| Disabled | keeps the settings and repeats nothing |
Every interface the repeater uses needs an address of each family it repeats: the form says which interface is missing one before anything is saved. Remove takes the repeater away after asking.
What it costs#
Listing only the services you need — AirPlay and printing, say, but not file shares — keeps the rest of what the trusted network announces to itself.
What breaks if you get it wrong#
- The wrong pair. Repeating between the LAN and the WAN puts your own announcements on the provider's network.
- Firewall rules that do not follow. Discovery works and connecting does not: the device appears in the list and times out when chosen.
- An interface without an address of the family. The form refuses it; the router would refuse the change.
- Expecting it to route. The repeater carries discovery. If the two networks cannot reach each other, finding a service does not let you use it.