netplan ignores NetworkManager ipv4.route-metric

[Alexandru Cheltuitor]

[Impact]
Dummy (what I've mainly tested) connections are not being passed the ipv4.route-metric value from NM, instead they have the default value of 550, though this behavior was not observed with the IPv6 protocol.

[Test case]
On Ubuntu 24.04:

1) Create dummy connection via nmcli: nmcli c a type dummy ifname pvpnksintrf0 con-name pvpn-killswitch ipv4.method manual ipv4.addresses "100.85.0.1/24" ipv4.gateway "100.85.0.1" ipv6.method manual ipv6.addresses "fdeb:446c:912d:08da::/64" ipv6.gateway "fdeb:446c:912d:08da::1" ipv4.route-metric 98 ipv6.route-metric 95

2) Run the command to show connection info: nmcli c s pvpn-killswitch

2.1) Notice that ipv6.route-metric has been taken but not ipv4.route-metric, even though the data is present under /etc/netplan/90*.yml

Additionally:
If I configure the dummy connection via netplan and for the ipv4.route-metric to take effect, I need to either pass dhcp4: true (by switching ipv4.method auto, though this other implications when IPv6 is disabled at kernel level) or ipv4.route-metric: 98 in the pass-through section (to which I don't have access via NM).

The current behavior breaks the Proton VPN linux app on all Ubuntu 24.04 machines.

[Danilo Egea Gondolfo (danilogondolfo)]

Hello, thanks for bringing this issue to our attention and working on a fix for it.

I saw that you created a PR on Github as well [1] (which is the preferred way of submitting patch to Netplan). I just left some comments there.

Thanks!

[1] - https://github.com/canonical/netplan/pull/495

[Lukas Märdian (slyon)]

https://github.com/canonical/netplan/pull/495

[Lukas Märdian (slyon)]

released in v1.1