Comment 1 for bug 1852504

I actually am not sure if the port status as ACTIVE/DOWN even matters. In my case VM has nameserver 10.128.144.23 as 2nd entry and it is in status DOWN.

I think problem is on agent side here. It appends all ports to list of dns-server DHCP option to advertise, based only on if the device_owner field is "network:dhcp". It doesn't take into account reserved port or status:

https://github.com/openstack/neutron/blob/stable/rocky/neutron/agent/linux/dhcp.py#L1089