+++ This bug was initially created as a clone of Bug #1761389 +++

Description of problem:

If we attach a subnet to that external network afterwards, the northbound
database loses that logical port, together with the row in the gateway_chassis table.

Version-Release number of selected component (if applicable):
OSP13 (all versions)

How reproducible:
Always

Steps to Reproduce:

openstack network create public --external --default --provider-network-type vlan --provider-physical-network tenant --provider-segment 1099

openstack router create myrouter

EXT_NET_ID=$(openstack network show public -f value -c id)
openstack router set --external-gateway $EXT_NET_ID myrouter

Actual results:

We lose connectivity on all external subnets, because the router logical port is lost

Expected results:

User should be able to set subnets after creating and attaching external networks to router


Additional info:

See launchpad for more details on what the sequence of events cause this.