I have a use case where an instance is connected to a shared network and an internal network.

The internal network is routed and the shared network is used to access a security management appliance with no router configured. Because of this I advertise the DNS servers on the internal network and I configure the shared network without DNS servers.

In the case you configure a subnet without an explicit list of DNS servers the dnsmasq implementation of the dhcp agent (tested in Juno and Mitaka) will advertise itself as a DNS server polluting the resolve.conf of the instance and occasionally leading to DNS response delays because the dnsmasq process does not have forwarders configured.

Is there a way to tell neutron (or the dhcp agent) to completely forgo the DNS answers and only give out DHCP addresses for a network without explicit DNS entries ?