Comment 5 for bug 1833193

Thanks! that clarifies it - I think this is a bug upstream with systemd.

> if I set "dhcp4: no" explicit when confiugring static addressing, it behaves as expected

are you sure? that isn't what I would expect, it seems the problem is networkd doesn't adjust the address lifetime when networkd is restarted and the address changes from dhcp->static; i would not expect the DHCP=no param it fix that. Although that's a netplan config, so possibly netplan does something additional under the covers, other than what systemd-networkd does.

> It seems like upon a restart, systemd-networkd will allways add whatever IP config it had before the service stopped, and then apply changes

not exactly, what's happening is when you stop networkd, it does not remove network configuration that it manages, so in this case it would leave the dhcp address on the interface. then when you (re)start networkd, it does not change existing addresses that it manages, so it sees that the interface already has the address that it's been configured to use as a static address, and does not change it. It looks like networkd needs to also check the address's lifetime to make sure static addrs have their lifetime set to 'forever' (I have not actually checked the code yet to verify this).

If you reboot, or manually remove the address, or just bring the interface down and back up, networkd will re-add the address with 'forever' lft, so this should only be a problem when you have manually changed the config for an address from dhcp->static using the same ip address, and then restart networkd without rebooting, at least IIUC.