A standalone EH1000v directly interacts with the license server for initial Product Key registration and continued license validation. It is required to have a DNS server set and reachable by the ExtraHop Appliance. The DNS Server needs to be able to resolve *.extrahop.com. The ExtraHop does not need port 53 access to the outside world, it only needs to be able to perform DNS queries against the defined DNS server. It essentially communicates with the License Server via the DNS server.
A clustered EH1000v and Appliance will use the ECM for registration and validation. The ECM is required to have an accessible DNS server that can resolve *.extrahop.com configured in the Network Connectivity page.