Comment 2 for bug 1826419

Fairly; I was able to reproduce the mismatch even without designate; specifically:

/etc/neutron/plugins/ml2/ml2_conf.ini

 [ml2]
 extension_drivers = port_security,dns_domain_ports

/etc/neutron/neutron.conf

 [DEFAULT]
 dns_domain = jamespage.example.

I then updated the dns_domain on the private network:

 openstack network set private --dns-domain designate.example.

and booted a couple of instances:

$ dnsmasq --no-hosts --pid-file=/opt/stack/data/neutron/dhcp/e2637497-2ed8-4a08-9cca-9b2cd86accd1/pid --dhcp-hostsfile=/opt/stack/data/neutron/dhcp/e2637497-2ed8-4a08-9cca-9b2cd86accd1/host --addn-hosts=/opt/stack/data/neutron/dhcp/e2637497-2ed8-4a08-9cca-9b2cd86accd1/addn_hosts --dhcp-optsfile=/opt/stack/data/neutron/dhcp/e2637497-2ed8-4a08-9cca-9b2cd86accd1/opts --dhcp-leasefile=/opt/stack/data/neutron/dhcp/e2637497-2ed8-4a08-9cca-9b2cd86accd1/leases --dhcp-match=set:ipxe,175 --dhcp-userclass=set:ipxe6,iPXE --local-service --bind-interfaces --dhcp-range=set:tag1,10.0.0.0,static,255.255.255.192,86400s --dhcp-option-force=option:mtu,1450 --dhcp-lease-max=64 --conf-file= --domain=designate.example.

$ cat /opt/stack/data/neutron/dhcp/e2637497-2ed8-4a08-9cca-9b2cd86accd1/host
fa:16:3e:9f:cf:f8,host-10-0-0-1.jamespage.example.,10.0.0.1
fa:16:3e:c3:0e:f7,host-10-0-0-2.jamespage.example.,10.0.0.2
fa:16:3e:4d:fc:2f,testserver-1.jamespage.example.,10.0.0.10
fa:16:3e:41:f8:61,testserver-2.jamespage.example.,10.0.0.32

you can clearly see that the entries in the host file are based on the configured jamespage.example. but that the domain is set to designate.example. as configured on the network.

This generates the forward/reverse DNS lookup mismatch from an instance perspective.

The dns_assignment of one of the servers ports looks like:

| dns_assignment | fqdn='testserver-1.jamespage.example.', hostname='testserver-1', ip_address='10.0.0.10' |

this is used to populate the dnsmasq host file.