Enable multicast DNS on Ubuntu Server

ubuntu-server-multicast-dns.md

Enabling multicast DNS (mDNS) on a server allows other hosts on the local network to address the server as <hostname>.local.

mDNS is disabled by default in Ubuntu Server:

$ resolvectl mdns
Global: no
Link 2 (eno1): no

mDNS setup involves two config changes:

Multicast DNS will be enabled on a link only if the per-link and the global setting is on.

First, enable mDNS globally in /etc/systemd/resolved.conf:

[Resolve]
...
MulticastDNS=yes
...

Next, we have to enable mDNS on the network interface. Ubuntu Server uses netplan to render network config files into /run/systemd/network. But netplan doesn't yet support mDNS configuration, so we need to augment the main network file with a drop-in file.

Determine the name of the main network file:

$ ls /run/systemd/network
10-netplan-eno1.network

Create the drop-in directory based on the name of the main network file:

$ mkdir /etc/systemd/network/10-netplan-eno1.network.d

Create the drop-in file at /etc/systemd/network/10-netplan-eno1.network.d/override.conf containing:

[Network]
MulticastDNS=yes

Reboot to apply the new configuration.

Verify that mDNS is enabled:

$ resolvectl mdns
Global: yes
Link 2 (eno1): yes

I edited the resolved.conf like shown here and did:
sudo resolvectl mdns enp2s0 true
And thats it, just replace enp2s0 with your interface. No need to reboot.