To resolve internal hostnames using internal DNS servers for remotely connected endpoints, the following two components must be configured on FortiSASE:
Split DNS Rules:
Split DNS allows the configuration of specific DNS queries to be directed to internal DNS servers instead of public DNS servers.
This ensures that internal hostnames are resolved using the organization's internal DNS infrastructure, maintaining privacy and accuracy for internal network resources.
Split Tunneling Destinations:
Split tunneling allows specific traffic (such as DNS queries for internal domains) to be routed through the VPN tunnel while other traffic is sent directly to the internet.
By configuring split tunneling destinations, you can ensure that DNS queries for internal hostnames are directed through the VPN to the internal DNS servers.
Reference:
FortiOS 7.2 Administration Guide: Provides details on configuring split DNS and split tunneling for VPN clients.
FortiSASE 23.2 Documentation: Explains the implementation and configuration of split DNS and split tunneling for securely resolving internal hostnames.

Reference:
FortiOS 7.2 Administration Guide: Provides details on configuring Secure Private Access and integrating with FortiGate.
FortiSASE 23.2 Documentation: Explains how to set up and manage connections between FortiSASE and corporate FortiGate.