Comment 2 for bug 1888666

Release: queens
command1: openstack network set --disable $uuid
command2: openstack network set --enable $uuid

Disabling the network reaches this code in the dhcp-agent:
https://github.com/openstack/neutron/blob/stable/queens/neutron/agent/dhcp/agent.py#L391-L396

Which calls "disable" on the agent(s), which comes down here
https://github.com/openstack/neutron/blob/stable/queens/neutron/agent/linux/dhcp.py#L254-L255

This, through
https://github.com/openstack/neutron/blob/stable/queens/neutron/agent/linux/dhcp.py#L260
comes to
https://github.com/openstack/neutron/blob/stable/queens/neutron/agent/linux/dhcp.py#L1584-L1585
which deletes the ports in
https://github.com/openstack/neutron/blob/stable/queens/neutron/api/rpc/handlers/dhcp_rpc.py#L237-L247

If there are no ports left in the network, in a hierarchical port-binding setup
one can free the segment of the network again, as it's unused. This would lead
to a vlan tag change, which the linux-bridge-agent does recognise, as it
creates the new interface for it - it just doesn't remove the old one.