[Bug 1812760] Re: networkd: [Route] PreferredSource not working in *.network files

[Dan Streetman]

bionic:

root at systemd-b:~# dpkg -l | grep libsystemd0
ii  libsystemd0:amd64               237-3ubuntu10.13                            amd64        systemd utility library
root at systemd-b:~# netplan apply
root at systemd-b:~# ip -6 r
fd8f:1d7d:b141::/64 dev ens3 proto kernel metric 256 pref medium
fe80::/64 dev ens3 proto kernel metric 256 pref medium


root at systemd-b:~# dpkg -l | grep libsystemd0
ii  libsystemd0:amd64               237-3ubuntu10.14                            amd64        systemd utility library
root at systemd-b:~# netplan apply
root at systemd-b:~# ip -6 r
a::/16 via fd8f:1d7d:b141::1 dev ens3 proto static src fd8f:1d7d:b141::2 metric 1024 pref medium
fd8f:1d7d:b141::/64 dev ens3 proto static src fd8f:1d7d:b141::2 metric 255 pref medium
fd8f:1d7d:b141::/64 dev ens3 proto kernel metric 256 pref medium
fe80::/64 dev ens3 proto kernel metric 256 pref medium

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https://bugs.launchpad.net/bugs/1812760

Title:
  networkd: [Route] PreferredSource not working in *.network files

Status in systemd:
  Unknown
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  Fix Committed
Status in systemd source package in Cosmic:
  Fix Committed
Status in systemd source package in Disco:
  Fix Released

Bug description:
  [Impact]

  Users cannot create IPv6 routes that specify PreferredSource. This
  means that users cannot specify a number of valid IPv6 routes that are
  useful in some circumstances. These routes can be created with the
  'ip' tool, just not with systemd.

  This was reported upstream in systemd issue #5882 is fixed by pulling
  in the changes in systemd PR #11375 -
  https://github.com/systemd/systemd/pull/11375

  [Test Case]

  Start a Bionic or Cosmic VM.

  Add the following netplan yaml (adjust for ethernet card and MAC):

  network:
      version: 2
      ethernets:
          ens3:
              dhcp4: true
              match:
                  macaddress: 52:54:00:e2:c2:d7
              set-name: ens3
              addresses: ["fd8f:1d7d:b141::2/64", "fd8f:1d7d:b141::200/64"]
              routes:
                - to: "a::/16"
                  via: "fd8f:1d7d:b141::1"
                  from: "fd8f:1d7d:b141::2"
                - to: "fd8f:1d7d:b141::/64"
                  scope: link
                  from: "fd8f:1d7d:b141::2"
                  metric: 255

  Run netplan apply or reboot. Wait ~10s.

  Currently, ip -6 route will not include a route to "a::/16", and will
  not include the route to "fd8f:1d7d:b141::/64" that has
  "fd8f:1d7d:b141::2" as the source address - both those addresses will
  be missing.

  Correct behaviour is for ip -6 route to report the following:

  ubuntu at b-np:~$ ip -6 route
  a::/16 via fd8f:1d7d:b141::1 dev ens3 proto static src fd8f:1d7d:b141::2 metric 1024 pref medium
  fd8f:1d7d:b141::/64 dev ens3 proto static src fd8f:1d7d:b141::2 metric 255 pref medium
  fd8f:1d7d:b141::/64 dev ens3 proto kernel metric 256 pref medium
  fe80::/64 dev ens3 proto kernel metric 256 pref medium

  Check before and after upgrade that 'systemctl status network-
  online.target' shows that the target has been reached.

  [Regression Potential]

  This changes the state machine in systemd which configures the links.
  It passes systemd's internal tests, and has been approved by systemd
  maintainers, but it remains possible that the changes will break the
  configuration of obscure network setups.

  The backport requires pulling in two further commits that also change
  behaviour: currently systemd deletes all addresses and routes that
  were attached to an interface. With this change, it will only delete
  those that are not specified in the configuration files. A side effect
  of this is that restarting networkd will not cause remove/add netlink
  events to be emitted for these addresses, so if anyone is relying on
  this behavior this will break compatibility; but that is an unlikely
  thing to be relying on, and it seems worth this risk to reduce
  unnecessary network state changes.

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