Cisco Secure Client
The Cisco Secure Client Umbrella Roaming Security module uses standard DNS ports 53/UDP and 53/TCP to communicate with Secure Access. If you explicitly block access to third-party DNS servers on your corporate or home network, you must allow certain CIDRs on the ports and protocols in your firewall.
In circumstances where third-party DNS servers are blocked, the Cisco Secure Client Umbrella Roaming Security module transitions to a state where it temporarily uses the DHCP-delegated DNS servers for resolution.