Interfaces configured as "Disconnected" not disabled in netplan

[Stéphane Graber]

Somewhat related to https://bugs.launchpad.net/maas/+bug/1832855 but in my case the issue is a bit different.

We have hardware used for network testing which has a LOT of network interfaces of various types, some are connected to non-MAAS managed networks which provide IPv6 SLAAC.

What we need is a way to indicate in MAAS that those interfaces should NOT have any connectivity configured, preferably they should be kept in the DOWN state or be explicitly configured in netplan to not be pulling any type of address with:
 - accept_ra: false
 - dhcp: false
 - dhcp6: false

Not doing this effectively breaks IPv6 connectivity as one of those interfaces just grabs an address and default gateway from an incoming router advertisement and ends up preferring that path over the one through the MAAS managed network, preventing any access to the system over IPv6.

[Björn Tillenius (bjornt)]

Adding the explicit config is probably the easiest solution for now. Although, I wonder, shouldn't this be the default in netplan?