Wandering Thoughts archives

Using Netplan to set up WireGuard on Ubuntu 22.04 works, but has warts

For reasons outside the scope of this entry, I recently needed to set up WireGuard on an Ubuntu 22.04 machine. When I did this before for an IPv6 gateway, I used systemd-networkd directly. This time around I wasn't going to set up a single peer and stop; I expected to iterate and add peers several times, which made netplan's ability to update and re-do your network configuration look attractive. Also, our machines are already using Netplan for their basic network configuration, so this would spare my co-workers from having to learn about systemd-networkd.

Conveniently, Netplan supports multiple configuration files so you can put your WireGuard configuration into a new .yaml file in your /etc/netplan. The basic version of a WireGuard endpoint with purely internal WireGuard IPs is straightforward:

network:
  version: 2
  tunnels:
    our-wg0:
      mode: wireguard
      addresses: [ 192.168.X.1/24 ]
      port: 51820
      key:
        private: '....'
      peers:
        - keys:
            public: '....'
          allowed-ips: [ 192.168.X.10/32 ]
          keepalive: 90
          endpoint: A.B.C.D:51820

(You may want something larger than a /24 depending on how many other machines you think you'll be talking to. Also, this configuration doesn't enable IP forwarding, which is a feature in our particular situation.)

If you're using netplan's systemd-networkd backend, which you probably are on an Ubuntu server, you can apparently put your keys into files instead of needing to carefully guard the permissions of your WireGuard /etc/netplan file (which normally has your private key in it).

If you write this out and run 'netplan try' or 'netplan apply', it will duly apply all of the configuration and bring your 'our-wg0' WireGuard configuration up as you expect. The problems emerge when you change this configuration, perhaps to add another peer, and then re-do your 'netplan try', because when you look you'll find that your new peer hasn't been added. This is a sign of a general issue; as far as I can tell, netplan (at least in Ubuntu 22.04) can set up WireGuard devices from scratch but it can't update anything about their WireGuard configuration once they're created. This is probably be a limitation in the Ubuntu 22.04 version of systemd-networkd that's only changed in the very latest systemd versions. In order to make WireGuard level changes, you need to remove the device, for example with 'ip link del dev our-wg0' and then re-run 'netplan try' (or 'netplan apply') to re-create the WireGuard device from scratch; the recreated version will include all of your changes.

(The latest online systemd.netdev manual page says that systemd-networkd will try to update netdev configurations if they change, and .netdev files are where WireGuard settings go. The best information I can find is that this change appeared in systemd v257, although the Fedora 41 systemd.netdev manual page has this same wording and it has systemd '256.11'. Maybe there was a backport into Fedora.)

In our specific situation, deleting and recreating the WireGuard device is harmless and we're not going to be doing it very often anyway. In other configurations things may not be so straightforward and so you may need to resort to other means to apply updates to your WireGuard configuration (including working directly through the 'wg' tool).