Hi,
You mean that it is possible to later make that VM port (created by nova) a parent port of a trunk? That is not supported in ml2/ovs (or it was not before), I never tried with OVN
the behavior should not depend on the backend used.
But it does and for good reason.
Ideally we wanted all drivers to allow putting a trunk even on a bound port. But for ovs that would have required unfeasible complexity of re-wiring upgrades (and network downtime while that re-wiring happens).
Even in the api-ref we have error code 409 with reason "A system configuration prevents the operation from succeeding":
https://docs.openstack.org/api-ref/network/v2/?expanded=create-trunk-detail
The gist of my point in the other sub-thread was that an already bound port can be made parent of a trunk with most drivers (except ml2/ovs). But if you do this on a nova-created port (as opposed to a port created manually or by anybody but nova) then nova won't be able to delete that port when deleting the vm.
Cheers, Bence