[Bug 1833193] Re: systemd-networkd fails to apply static IPv4 when the static IP is the same as previously configured by DHCP

[Dan Streetman]

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.

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https://bugs.launchpad.net/bugs/1833193

Title:
  systemd-networkd fails to apply static IPv4 when the static IP is the
  same as previously configured by DHCP

Status in systemd package in Ubuntu:
  New

Bug description:
  In bionic, running systemd 237-3ubuntu10.22 and netplan.io
  0.97-0ubuntu1~18.04.1, systemd-networkd fails to configure an
  interface with a static IPv4 address if the statically confiugred
  address is the same as the interface already has gotten from DHCP.

  This will cause the interface to loose its IP address when the DHCP
  lease exires, even though you've told netplan to configure it as
  static.

  I expect systemd-networkd to actually configure an IP address as
  static, regardless of what address the interface has before from DHCP.

  # lsb_release  -rd
  Description:	Ubuntu 18.04.2 LTS
  Release:	18.04

  # apt-cache policy systemd
  systemd:
    Installed: 237-3ubuntu10.22

  # apt-cache policy netplan.io
  netplan.io:
    Installed: 0.97-0ubuntu1~18.04.1

  A paste of systemd-networkd's debug log when I run "netplan apply" and
  the interface already has the static IP configured from DHCP.

  It seems like upon a restart, systemd-networkd will allways add
  whatever IP config it had before the service stopped, and then apply
  changes (if any). Since my new config has the same IP as it already
  had, it does nothing even though the new config has static
  configuration.

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