Comment 12 for bug 1857026

Deployed focal-ussuri from charm-neutron-api-plugin-ovn gate tests and applied pending Neutron patch [0].

With two instances running we can see the following information in the OVN DB:
$ sudo ovn-nbctl list dns
_uuid : d51565b8-4ddb-4038-8a92-55e25247a419
external_ids : {ls_name=neutron-de1d0eb4-405a-4fc1-98ef-b93c7a2a4524}
records : {"114.0.168.192.in-addr.arpa"=zaza-neutrontests-ins-1.openstack.example, "13.0.168.192.in-addr.arpa"=zaza-neutrontests-ins-2.openstack.example, zaza-neutrontests-ins-1="192.168.0.114", zaza-neutrontests-ins-1.openstack.example="192.168.0.114", zaza-neutrontests-ins-2="192.168.0.13", zaza-neutrontests-ins-2.openstack.example="192.168.0.13"}

Control test:
From instance forward DNS lookups of other instance names work:
$ host zaza-neutrontests-ins-1.openstack.example
zaza-neutrontests-ins-1.openstack.example has address 192.168.0.114

But reverse DNS lookup of other instance IP does not work:
$ host 192.168.0.114
Host 114.0.168.192.in-addr.arpa. not found: 3(NXDOMAIN)

Upgrade to packages from -proposed:
$ juju run --application ovn-chassis 'dpkg -l | grep ovn'
- Stdout: |
    ii neutron-ovn-metadata-agent 2:16.4.2-0ubuntu1 all Neutron is a virtual network service for Openstack - OVN metadata agent
    ii ovn-common 20.03.2-0ubuntu0.20.04.3 amd64 OVN common components
    ii ovn-host 20.03.2-0ubuntu0.20.04.3 amd64 OVN host components
  UnitId: ovn-chassis/0
- Stdout: |
    ii neutron-ovn-metadata-agent 2:16.4.2-0ubuntu1 all Neutron is a virtual network service for Openstack - OVN metadata agent
    ii ovn-common 20.03.2-0ubuntu0.20.04.3 amd64 OVN common components
    ii ovn-host 20.03.2-0ubuntu0.20.04.3 amd64 OVN host components
  UnitId: ovn-chassis/1

Confirm updated packages work:
$ sudo systemctl restart systemd-resolved
$ host zaza-neutrontests-ins-1.openstack.example
zaza-neutrontests-ins-1.openstack.example has address 192.168.0.114
$ host 192.168.0.114
114.0.168.192.in-addr.arpa domain name pointer zaza-neutrontests-ins-1.openstack.example.

0: curl https://review.opendev.org/changes/openstack%2Fneutron~823631/revisions/2/patch?download|base64 -d|sudo patch -p2