[Bug 1800836] Re: systemd-networkd doesn't process IPv6 RA properly

[Anton]

We are also affected by this issue. networkd does not expire routes
which causes issues with active-passive router configurations.

For me it looks like the issue is fixed in this pull request:
https://github.com/systemd/systemd/pull/3242

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https://bugs.launchpad.net/bugs/1800836

Title:
  systemd-networkd doesn't process IPv6 RA properly

Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  The gateways/firewalls in our DC are highly available and when there
  is a failover their IPv6 VIP (fe80::1) moves from the master to the
  backup one.

  We found that only our Bionic VMs behind those gateways had issues
  after a failover. Those Bionic VMs were all running systemd-networkd
  (from netplan) and before the failover they had:

  $ ip -6 route
  ...
  default via fe80::1 dev eth0 proto ra metric 1024 pref medium

  But after a failover:

  $ ip -6 route
  ...
  default proto ra metric 1024
          nexthop via fe80::1 dev eth0 weight 1
          nexthop via fe80::210:18ff:febe:6750 dev eth0 weight 1

  And after another failover:

  $ ip -6 route
  ...
  default proto ra metric 1024
          nexthop via fe80::1 dev eth0 weight 1
          nexthop via fe80::210:18ff:febe:6750 dev eth0 weight 1
          nexthop via fe80::210:18ff:fe77:b558 dev eth0 weight 1

  
  This is problematic as those then use fe80::210:18ff:fe77:b558%$IFACE as their default gateway even when this gateway is unavailable:

  $ ip -6 route get ::
  :: from :: via fe80::210:18ff:fe77:b558 dev eth0 proto ra src fe80::a800:ff:fe51:8c37 metric 1024 pref medium

  
  We concluded it was a systemd-networkd bug after checking that the following combinations were NOT affected:

  1) Xenial+4.4 kernel
  2) Xenial+4.15 kernel
  3) Bionic+ifupdown

  
  Additional information:

  $ apt-cache policy systemd
  systemd:
    Installed: 237-3ubuntu10.3
    Candidate: 237-3ubuntu10.3
    Version table:
   *** 237-3ubuntu10.3 500
          500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       237-3ubuntu10 500
          500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages

  $ lsb_release -rd
  Description:	Ubuntu 18.04.1 LTS
  Release:	18.04

  ProblemType: Bug
  DistroRelease: Ubuntu 18.04
  Package: systemd 237-3ubuntu10.3
  ProcVersionSignature: Ubuntu 4.15.0-38.41-generic 4.15.18
  Uname: Linux 4.15.0-38-generic x86_64
  ApportVersion: 2.20.9-0ubuntu7.4
  Architecture: amd64
  Date: Wed Oct 31 08:47:28 2018
  Lspci: Error: [Errno 2] No such file or directory: 'lspci': 'lspci'
  Lsusb: Error: [Errno 2] No such file or directory: 'lsusb': 'lsusb'
  MachineType: QEMU Standard PC (i440FX + PIIX, 1996)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.15.0-38-generic root=UUID=43b7ee2e-2ab1-4505-8e0b-d9fe0563a034 ro console=ttyS0 net.ifnames=0 vsyscall=none kaslr nmi_watchdog=0 possible_cpus=1
  SourcePackage: systemd
  UpgradeStatus: No upgrade log present (probably fresh install)
  dmi.bios.date: 04/01/2014
  dmi.bios.vendor: SeaBIOS
  dmi.bios.version: Ubuntu-1.8.2-1ubuntu1
  dmi.chassis.type: 1
  dmi.chassis.vendor: QEMU
  dmi.chassis.version: pc-i440fx-xenial
  dmi.modalias: dmi:bvnSeaBIOS:bvrUbuntu-1.8.2-1ubuntu1:bd04/01/2014:svnQEMU:pnStandardPC(i440FX+PIIX,1996):pvrpc-i440fx-xenial:cvnQEMU:ct1:cvrpc-i440fx-xenial:
  dmi.product.name: Standard PC (i440FX + PIIX, 1996)
  dmi.product.version: pc-i440fx-xenial
  dmi.sys.vendor: QEMU

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