Comment 12 for bug 1772859

> We added interfaces to the file /etc/network/interfaces.
> So NM is not able to manage the interfaces updated in the said file.
> When we removed the interfaces from the above file, It started working.
>
> Is this approach correct ??

Yes.

NetworkManager, as shipped in Ubuntu, comes with multiple plugins and has networkd/ifupdown co-operation enabled by default. Out of the box, NetworkManager will not manage any regular eth devices that are already managed by somebody else which includes networkd and ifupdown. One should only ever configure one device using one of the technologies, as usually, multiple configurations of the same device using different stacks is an indication of a configuration mistake.

For the eth devices, we currently prefer networkd&ifupdown, over NM. And the preference of wifi/3g/4g/lte-like adhoc devices is with NM, over other stacks.

If you are exercising testing of various stacks, do ensure you cleanup systems to a pristine state, without any configs, for any of the stacks first, before proceeding automating using a specific network stack.

Removing or not installing netplan, should not be required to achieve what you want. All Ubuntu systems should have ubuntu-minimal meta-package installed, which means netplan.io package should be left installed too. Remvoing / not-installing ubuntu-minimal, may result in upgrade and runtime issues, as such systems are harder to correctly support. Please evaluate and ensure that ubuntu-minimal is installed in your case. Given NetworkManager usage, it shouldn't add too much cruft, if installed without recommends.