Bionic: interface stuck in state "configuring" on a VM with two NICs, DHCP, and the secondary NIC configured to ignore routes from DHCP

[Michael Steffens]

[Impact]

Network interfaces not using route information from DHCP4 do not reach configured state, but remain 'configuring' on Bionic.

[Test Case]

 1) Launch a VM with two network interfaces connected to ports on distinct network, each configured using DHCP4.

 2) Configure systemd-networkd to set up both interfaces via DHCP, but to ignore DHCP route information (plus possibly other system wide configuration supposed to be unambiguous, like DNS) from secondary interface. You can do so
    * either directly in /etc/systemd/network/, as shown in https://github.com/systemd/systemd/issues/9289,
    * or via netplan.io 0.96-0ubuntu0.18.04.2, as shown in https://bugs.launchpad.net/netplan/+bug/1759014/comments/48.

 3) Reboot.

 4) Both interfaces should now be reported as configured:

    # networkctl -a
    IDX LINK TYPE OPERATIONAL SETUP
      1 lo loopback carrier unmanaged
      2 ens3 ether routable configured
      3 ens4 ether routable configured

    3 links listed.

[Other Info]

The issue is known for systemd releases before 239, and was fixed with https://github.com/systemd/systemd/commit/223932c786ada7f758a7b7878a6ad2dae0d1e5fb.

I have tested it by manually merging that fix into sources of systemd 237-3ubuntu10.15, rebuilding and installing the package. Worked fine.

See also https://bugs.launchpad.net/netplan/+bug/1759014 and https://bugs.launchpad.net/netplan/+bug/1776228.

[Dan Streetman (ddstreet)]

commit 223932c786ada7f758a7b7878a6ad2dae0d1e5fb was just added to systemd in bionic via bug 1804478.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.