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

@gkapellmann yeah, if network is managed by systemd-networkd, then you need to create a drop-in setting to enable mDNS explicitly as defined above. netplan status tells if an interface is managed by NetworkManager or networkd.

On one of my hosts (with ubuntu-desktop component):

●  4: wlp94s0 wifi UP (NetworkManager: wlp94s0)

On another host (without ubuntu-desktop component):

●  2: enp1s0 ethernet UP (networkd: enp1s0)

Note that I had to explicitly stop and disable systemd-networkd service after I installed ubuntu-desktop. So if systemd-networkd is active it's not necessarily means networkd manages the network.

On the first host managed by NetworkManager it's sufficient to only change /etc/systemd/resolved.conf and restart systemd-resolved.
On the second host there's a need to create a override.conf as described in the gist and restart both systemd-resolved and systemd-networkd. A reboot is not mandatory to apply the changes.

Right! I had done this before and didnt work... beacuse I had a one letter typo in the override.conf directory... my bad!

But learning this NetworkManager vs networkd detail has been very helpful!

Thank you for yor time!

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.