Threat Prevention - Network is configured on your DNS Server(s) and forwards DNS queries to the HEIMDAL DNS Resolvers which are responsible for filtering all network packages based on DNS request origin and destination.
In the situation, you are registering DNS errors (or timeouts), we recommend the following DNS fallback methods:
1. Changing the DNS Forwarder(s)
2. Enabling Hybrid DNS to achieve DNS filtering at the DNS Server level
Changing the DNS Forwarder(s)
You can supplement the Heimdal DNS Resolvers (220.127.116.11 and 18.104.22.168) with the Google DNS Resolvers or any other public DNS Resolver to temporarily solve the problem:
Enabling Hybrid DNS to achieve DNS filtering at the DNS Server level
Instead of using the Threat Prevention Network DNS Resolvers, you can enable Hybrid DNS (in the Heimdal Dashboard -> Network Settings -> Threat Prevention -> DarkLayer Guard) that will allow you to use the Heidmal LogAgent installed on the DNS Server to filter DNS traffic coming from within the environment.