Comment 2 for bug 1944083

looking at the metadata code this is where we generate the dns info

https://github.com/openstack/nova/blob/50fdbc752a9ca9c31488140ef2997ed59d861a41/nova/virt/netutils.py#L103-L121

       if subnet_v4:
            if subnet_v4.get_meta('dhcp_server') is not None:
                continue

            if subnet_v4['ips']:
                ip = subnet_v4['ips'][0]
                address = ip['address']
                netmask = model.get_netmask(ip, subnet_v4)
                if subnet_v4['gateway']:
                    gateway = subnet_v4['gateway']['address']
                broadcast = str(subnet_v4.as_netaddr().broadcast)
                dns = ' '.join([i['address'] for i in subnet_v4['dns']])
                for route_ref in subnet_v4['routes']:
                    (net, mask) = get_net_and_mask(route_ref['cidr'])
                    route = {'gateway': str(route_ref['gateway']['address']),
                             'cidr': str(route_ref['cidr']),
                             'network': net,
                             'netmask': mask}
                    routes.append(route)

so we just take the info from neutron and more or less use it directly

this resulted in a json blob that looks like this
https://specs.openstack.org/openstack/nova-specs/specs/liberty/implemented/metadata-service-network-info.html#rest-api-impact

which can be used by cloud init to configure networking

 { // Standard VM VIF networking
        "id": "private-ipv4",
        "type": "ipv4",
        "link": "interface0",
        "ip_address": "10.184.0.244",
        "netmask": "255.255.240.0",
        "dns_nameservers": [
            "69.20.0.164",
            "69.20.0.196"
        ],
        "routes": [
            {
                "network": "10.0.0.0",
                "netmask": "255.0.0.0",
                "gateway": "11.0.0.1"
            },
            {
                "network": "0.0.0.0",
                "netmask": "0.0.0.0",
                "gateway": "23.253.157.1"
            }
        ],
        "network_id": "da5bb487-5193-4a65-a3df-4a0055a8c0d7"
    },

we are not going to add any /32 routes to the name servers and will only populate teh "routes" section if the subnet had addtional routs popluated in neutron.

i suspect the issue you are fasing is in the neturon DHCP server or possible cloud init as nova is not going to activly push any rout infomation to the vm that would install a /32 directly.