[Bug 1859862] [NEW] networkd doesn't re-enable ipv6 unless mtu is set

[Dan Streetman]

Public bug reported:

[impact]

if the 'disable_ipv6' procfs setting is disabled, and networkd is
configured with ipv6 networking, networkd will not enable ipv6 via the
procfs setting unless the interface mtu is also set to a custom value,
that doesn't match the current interface mtu.

[test case]

TBD

[regression potential]

as this adjusts when the procfs 'disable_ipv6' setting is changed, the
regression potential could cause failure to properly set/create ipv6
addresses, or to leave ipv6 disabled entirely.

[scope]

This is needed in Bionic and Eoan.

the commit to fix this is 482efedc081b0c4bf2e77a3dee6b979d9c9a5765 which
is included starting in v243, so it is included already in Focal.

Ignoring Disco, as it is EOL next week.

This problem was introduced by commit
44b598a1c9d11c23420a5ef45ff11bcb0ed195eb, which was included starting in
v239, but also backported to Bionic in bug 1850704.

[other info]

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: Fix Released

** Affects: systemd (Ubuntu Bionic)
     Importance: Medium
     Assignee: Dan Streetman (ddstreet)
         Status: In Progress

** Affects: systemd (Ubuntu Disco)
     Importance: Undecided
         Status: Won't Fix

** Affects: systemd (Ubuntu Eoan)
     Importance: Medium
     Assignee: Dan Streetman (ddstreet)
         Status: In Progress

** Also affects: systemd (Ubuntu Eoan)
   Importance: Undecided
       Status: New

** Also affects: systemd (Ubuntu Bionic)
   Importance: Undecided
       Status: New

** Also affects: systemd (Ubuntu Disco)
   Importance: Undecided
       Status: New

** Changed in: systemd (Ubuntu Disco)
       Status: New => Won't Fix

** Changed in: systemd (Ubuntu Eoan)
       Status: New => In Progress

** Changed in: systemd (Ubuntu Bionic)
       Status: New => In Progress

** Changed in: systemd (Ubuntu)
       Status: New => Fix Released

** Changed in: systemd (Ubuntu Eoan)
   Importance: Undecided => Medium

** Changed in: systemd (Ubuntu Bionic)
   Importance: Undecided => Medium

** Changed in: systemd (Ubuntu Eoan)
     Assignee: (unassigned) => Dan Streetman (ddstreet)

** Changed in: systemd (Ubuntu Bionic)
     Assignee: (unassigned) => Dan Streetman (ddstreet)

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https://bugs.launchpad.net/bugs/1859862

Title:
  networkd doesn't re-enable ipv6 unless mtu is set

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  In Progress
Status in systemd source package in Disco:
  Won't Fix
Status in systemd source package in Eoan:
  In Progress

Bug description:
  [impact]

  if the 'disable_ipv6' procfs setting is disabled, and networkd is
  configured with ipv6 networking, networkd will not enable ipv6 via the
  procfs setting unless the interface mtu is also set to a custom value,
  that doesn't match the current interface mtu.

  [test case]

  TBD

  [regression potential]

  as this adjusts when the procfs 'disable_ipv6' setting is changed, the
  regression potential could cause failure to properly set/create ipv6
  addresses, or to leave ipv6 disabled entirely.

  [scope]

  This is needed in Bionic and Eoan.

  the commit to fix this is 482efedc081b0c4bf2e77a3dee6b979d9c9a5765
  which is included starting in v243, so it is included already in
  Focal.

  Ignoring Disco, as it is EOL next week.

  This problem was introduced by commit
  44b598a1c9d11c23420a5ef45ff11bcb0ed195eb, which was included starting
  in v239, but also backported to Bionic in bug 1850704.

  [other info]

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