[Bug 1867375] Re: systemd-networkd: UseRoutes behavior change with introduction of UseGateway param

[Brian Murray]

Hello Sunil, or anyone else affected,

Accepted systemd into eoan-proposed. The package will build now and be
available at https://launchpad.net/ubuntu/+source/systemd/242-7ubuntu3.9
in a few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.  Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested, what testing has been
performed on the package and change the tag from verification-needed-
eoan to verification-done-eoan. If it does not fix the bug for you,
please add a comment stating that, and change the tag to verification-
failed-eoan. In either case, without details of your testing we will not
be able to proceed.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance for helping!

N.B. The updated package will be released to -updates after the bug(s)
fixed by this package have been verified and the package has been in
-proposed for a minimum of 7 days.

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

** Tags removed: verification-done
** Tags added: verification-needed verification-needed-eoan

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https://bugs.launchpad.net/bugs/1867375

Title:
  systemd-networkd: UseRoutes behavior change with introduction of
  UseGateway param

Status in netplan.io package in Ubuntu:
  Confirmed
Status in systemd package in Ubuntu:
  Fix Released
Status in netplan.io source package in Bionic:
  Invalid
Status in systemd source package in Bionic:
  In Progress
Status in netplan.io source package in Eoan:
  Invalid
Status in systemd source package in Eoan:
  Fix Committed
Status in netplan.io source package in Focal:
  Confirmed
Status in systemd source package in Focal:
  Fix Committed
Status in netplan.io source package in Groovy:
  Confirmed
Status in systemd source package in Groovy:
  Fix Released

Bug description:
  [impact]

  the networkd UseRoutes parameter allowed ignoring all routes provided
  by a dhcp4 server, including the route via the dhcp4-provided gateway.
  This was the behavior of networkd until recently, and in Focal the
  UseRoutes parameter does *not* prevent networkd from adding the route
  via the dhcp4-provided gateway.  This is now controlled with a new
  parameter, UseGateway.

  The systemd in Focal unfortunately has part of the upstream code; it
  no longer ignores the gateway route when UseRoutes=false is specified,
  but also it does not include the UseGateway parameter.

  Before Focal, networkd did not allow ignoring dhcpv4 routes and the
  gateway separately; the UseRoutes= parameter either used, or ignored,
  both.  This is why upstream added the UseGateway= paramter, which
  should be backported to allow control of ignoring the dhcpv4 routes
  and gateway separately.

  [test case]

  In Focal, bug 1872589 has a good test case netplan config, but a very
  quick test can be done with the networkd config:

  [Match]
  Name=eth0

  [Network]
  DHCP=ipv4
  LinkLocalAddressing=ipv6

  [DHCP]
  RouteMetric=100
  UseMTU=true
  UseRoutes=false

  this results in the system incorrectly setting a route via the default
  gateway:

  root at lp1867375-f:~# ip r
  default via 10.202.51.1 dev eth0 proto dhcp src 10.202.51.86 metric 100
  10.202.51.0/24 dev eth0 proto kernel scope link src 10.202.51.86
  10.202.51.1 dev eth0 proto dhcp scope link src 10.202.51.86 metric 100

  Before Focal, the above test case shows "correct" behavior, but there
  is no way to ignore the dhcpv4 routes but use the dhcpv4 gateway.
  This pre-Focal, the test case would be to use the UseGateway=
  parameter, e.g.:

  [Match]
  Name=eth0

  [Network]
  DHCP=ipv4
  LinkLocalAddressing=ipv6

  [DHCP]
  RouteMetric=100
  UseMTU=true
  UseRoutes=false
  UseGateway=true

  which *should* result in the default gateway being configured:

  root at lp1867375-f:~# ip r
  default via 10.202.51.1 dev eth0 proto dhcp src 10.202.51.86 metric 100
  10.202.51.0/24 dev eth0 proto kernel scope link src 10.202.51.86
  10.202.51.1 dev eth0 proto dhcp scope link src 10.202.51.86 metric 100

  [regression potential]

  Any regression would likely involve incorrect setting, or ignoring, of
  dhcpv4-provided routes, and/or incorrect setting, or ignoring, of the
  dhcpv4-provided gateway.

  [scope]

  This is fixed by these upstream PRs:
  https://github.com/systemd/systemd/pull/15443
  https://github.com/systemd/systemd/pull/15136
  https://github.com/systemd/systemd/pull/14983

  Parts of all those PRs are required in Focal, Eoan, and Bionic.

  I am not fixing this for Xenial, at this time.

  For Debian, I opened this MR:
  https://salsa.debian.org/systemd-team/systemd/-/merge_requests/92

  For Groovy, I opened this MR:
  https://code.launchpad.net/~ddstreet/ubuntu/+source/systemd/+git/systemd/+merge/383661

  [other info]

  to properly support separation of 'routes' and 'gateways' received via
  dhcp4, SRU releases should also support the UseGateway parameter,
  which is what this bug was originally opened requesting.

  [original description]

  requesting backport of PR https://github.com/systemd/systemd/pull/14983 which fixes the issue described in
  https://github.com/systemd/systemd/issues/14982 to 18.04 (bionic)

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