[Bug 1872589] Re: systemd-networkd is not honoring UseRoutes=false

[Dan Streetman]

upstream systemd has actually changed the behavior of UseRoutes; now, it
only disables actual defined routes provided by dhcp, and does not
control the gateway route.  There is a new option, UseGateway, that
controls if the dhcp-provided gateway route should be used or not.

More details in bug 1867375 as well as references to the upstream
changes.  As noted in my comment there, if UseGateway is backported to
Bionic, its default needs adjustment to default to the provided value of
UseRoutes; maybe that should be done for Focal as well.

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Title:
  systemd-networkd is not honoring UseRoutes=false

Status in systemd package in Ubuntu:
  Triaged

Bug description:
  When netplan configures dhcp4-overrides and set "use-routes" to false,
  systemd-networkd should be configured with UseRoutes=false. It is.
  Unfortunately looks like systemd-networkd is not honoring it and
  configuring the default gateways for the interfaces no matter what.

  Ubuntu Focal: systemd: 245.4-2ubuntu1

  ----

  $ sudo cat /etc/netplan/50-cloud-init.yaml
  network:
      ethernets:
          enp5s0:
              match:
                  macaddress: 00:16:3e:af:c4:d6
              set-name: eth0
              dhcp4: true
              dhcp-identifier: mac
          enp6s0:
              match:
                  macaddress: 00:16:3e:50:11:9c
              set-name: iscsi01
              dhcp4: true
              dhcp-identifier: mac
              dhcp4-overrides:
                use-routes: false
          enp7s0:
              match:
                  macaddress: 00:16:3e:b3:cc:50
              set-name: iscsi02
              dhcp4: true
              dhcp-identifier: mac
              dhcp4-overrides:
                use-routes: false
      version: 2
      renderer: networkd

  ----

  $ cat /var/run/systemd/network/10-netplan-enp6s0.network

  [Match]
  MACAddress=00:16:3e:50:11:9c
  Name=iscsi01

  [Network]
  DHCP=ipv4
  LinkLocalAddressing=ipv6

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

  --

  $ ip route show | grep default
  default via 10.250.93.1 dev iscsi02 proto dhcp src 10.250.93.101 metric 100
  default via 10.250.94.1 dev iscsi01 proto dhcp src 10.250.94.167 metric 100
  default via 10.250.97.1 dev eth0 proto dhcp src 10.250.97.123 metric 100

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