Comment 4 for bug 1879673

I'd also add in the documentation at https://cloudinit.readthedocs.io/en/latest/topics/network-config-format-v2.html it's very unclear whether all the settings listed after "parameters" need to be nested under "parameters", because there are no examples of this.

In other words, it could be that the solution is to change

  br0:
    interfaces:
      - ens3
    forward-delay: 0
    stp: false
    accept-ra: false
    ...

to

  br0:
    interfaces:
      - ens3
    parameters:
      forward-delay: 0
      stp: false
    accept-ra: false
    ...

Of course, this bug still applies (you might not want to set any parameters at all).

On top of this, I think it would be be helpful if an error were reported when unknown parameters appear at the outer level.