port mDNS via balena tunnel

Product support
1

Hi,

We try to use mDNS to support additional domain names on the device. For example if we have a device with a hostname of HOST we would like to expose ui-host.local and login-host.local as mDNS names.

We created/used a docker container that adjusts the avahi daemon to know about these new names. When logged in to the device (ssh) we can PING these endpoints properly, so mDNS works. mDNS is from RFC6762 and broadcasts the names on port 5353

Now wondering if we can get these broadcasts over the balena tunnel as well?

We are simply using balena tunnel for systems not reachable on the local network (for example, because the device is in the office and a developer works from home).

balena tunnel -p 8080:8080 443:3001 etc

and use localhost:3001 to reach out to the HTTPS port of the device.

Now we would like to also be able to ping on the created mDNS names and tried to expose the port like this:

balena tunnel -p 8080:8080 443:3001 5353:5353

however we do not see the “PING ui-host.local” resulting in a reply. Should broadcasts from avahi be ported differently or are we missing something obvious?

2

mDNS works by your device sending a multicast packet on port 5353 asking for the device with the name foo.local to identify itself (hence the name, multicast DNS). This is different to your device sending a packet to every distinct IP address it can see on port 5353, and multicast packets won’t get sent over the Balena tunnel.

You could, in theory, write some software that listens for those packets and forwards them over the Balena tunnel, but for development purposes its probably easier to just add ui-host.local and login-host.local to /etc/hosts.