After installation, lxdbr0 is unmanaged by systemd-networkd

[kkovacs]

Required information

• Distribution: Ubuntu
• Distribution version: 24.04
• The output of "snap list --all lxd core20 core22 core24 snapd":

Name    Version         Rev    Tracking       Publisher   Notes
core22  20241119        1722   latest/stable  canonical✓  base
lxd     5.21.2-084c8c8  31214  5.21/stable/…  canonical✓  -
snapd   2.66.1          23258  latest/stable  canonical✓  snapd

• The output of "lxc info":
  lxc-info.txt

Issue description

Right after running snap init --auto, the lxdbr0 interface is in an unmanaged state by systemd-networkd:

root@test4 ~ [0]# networkctl
IDX LINK   TYPE     OPERATIONAL SETUP
  1 lo     loopback carrier     unmanaged
  2 eth0   ether    routable    configured
  3 eth1   ether    routable    configured
  4 lxdbr0 bridge   no-carrier  unmanaged

4 links listed.

After a reboot, or after running snap restart lxd, the lxdbr0 is configured:

root@test4 ~ [1]# networkctl
IDX LINK         TYPE     OPERATIONAL SETUP
  1 lo           loopback carrier     unmanaged
  2 eth0         ether    routable    configured
  3 eth1         ether    routable    configured
  4 lxdbr0       bridge   routable    configured
  6 vethce4689da ether    enslaved    unmanaged

This is a problem when one is trying to configure the lxdbr0 interface with systemd's .network files. For example, trying to set up the host machine's systemd-resolved's access to LXD's dnsmasq in /etc/systemd/network/lxdbr0.network.

Additional info: If one tries to run a networkctl reload, then the network seemingly gets into configured state, but the route to the network disappears. This is probably systemd's fault, not LXD's, but nevertheless, running a network reload is not enough.

Steps to reproduce

0. Get a fresh Ubuntu 24.04
1. snap install --classic lxd
2. snap init --auto
3. networkctl, see:

[...]
lxdbr0 bridge   no-carrier  unmanaged
[...]

[simondeziel]

From the systemd-networkd's perspective, the bridges created by LXD are effectively unmanaged.