[Bug 1804478] Re: netplan dhcp interface with no default route causes systemd-networkd-wait-online to hang

[Benjamin Drung]

Commit 223932c786ada7f758a7b7878a6ad2dae0d1e5fb [networkd: fix dhcp4
link without routes not being considered ready (#8728)]. Only systemd
release v239 contains this fix.

** No longer affects: systemd

** Also affects: systemd
   Importance: Undecided
       Status: New

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Title:
  netplan dhcp interface with no default route causes systemd-networkd-
  wait-online to hang

Status in systemd:
  New
Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  root cause in systemd bug:
  https://github.com/systemd/systemd/issues/3752

  Environment:
  Ubuntu 18.04 LTS amd64
  systemd package version 237-3ubuntu10.9

  How to trigger:
  1. add netplan interface with dhcpv4 client enabled:
          enp0s8:
              addresses: []
              dhcp4: true
  2. configure dhcp server to NOT give a default route, or any route for that matter
  3. reboot
  4. systemd-networkd-wait-online will block until dhcp renew is triggered
  root at sensor1:~# /lib/systemd/systemd-networkd-wait-online --timeout=3
  Event loop failed: Connection timed out
  root at sensor1:~# /lib/systemd/systemd-networkd-wait-online --timeout=3 --ignore=enp0s8
  managing: enp0s3
  ignoring: lo
  ignoring: enp0s8

  How to fix:
  Backport upstream changes from systemd (see related systemd ticket).

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