Private DNS will enable you to reach an internal resource by its hostname (as published by your local DNS server). This can ease your workflow, as you will no longer need to specify the resource's IP address and will be able to resolve local resources .
NOTE: Do not configure a public DNS server, as by default your traffic will be routed through one, in case the private DNS server are not able to resolve the address).
To configure the private DNS:
Navigate the Network| Tunnels
Edit the the Settings and choose Private DNS.
After defining the custom primary and secondary DNS addresses, this information will be highlighted on the Networks page.