SD-WAN is a networking component included in a SASE solution but not in an SSE solution. SSE focuses solely on security services (like ZTNA, SWG, and CASB), while SASE combines both networking (e.g., SD-WAN) and security into a unified cloud-delivered service.

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.
References:
FortiOS 7.6 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.

To use agentless private application access as shown, the Secure Private Access (SPA) feature must be enabled in FortiSASE, and the relevant FortiGate ZTNA application gateway must be configured to provide access to the private applications. Agentless access does not require FortiClient on the user device, and proxy/SSO configuration is not a prerequisite for this feature.

According to the NSE7 SASE Enterprise Guide (Pages 64 & 153) , FortiSASE utilizes an intelligent engine to manage connectivity to private resources through various selection methods:
* Hub Health and Priority: FortiSASE incorporates a built-in SD-WAN engine for intelligent routing selection among established IPsec links. The health check IP address periodically receives performance metrics, including jitter, latency, and packet loss, for each service connection. In this mode, FortiSASE evaluates the available hubs and selects the one with the highest priority (the most preferred value) within each POP, provided that the hub meets the defined service-level agreement (SLA) requirements . For this configuration to function correctly, both FortiSASE and the SPA hub must use the same Autonomous System Number (ASN).
* BGP Multiple Exit Discriminator (MED): This method leverages the standard BGP MED attribute, which allows an autonomous system to signal its preferred entry point to a peer. FortiSASE learns the MED values advertised by the configured hubs. The architecture is designed so that the lower the MED value , the more preferred the path is to the receiving router. Consistent with the " Zero Trust " and " Secure Access " principles, even when using BGP MED, the selection is gated by the health engine; therefore, the hub is only selected if it also satisfies the configured SLA thresholds .
While SLA thresholds can be configured, the primary logic for hub selection focuses on how priority and dynamic routing attributes (like MED) interact with the real-time health of the tunnel.

The VPN tunnel between the FortiSASE spoke and the FortiGate hub is not establishing due to the configuration of mode config, which is not supported by FortiSASE spoke devices. Mode config is used to assign IP addresses to VPN clients dynamically, but this feature is not applicable to FortiSASE spokes.
* Mode Config in IPsec:
* The configuration snippet shows that mode config is enabled in the IPsec phase 1 settings.
* Mode config is typically used for VPN clients to dynamically receive an IP address from the VPN server, but it is not suitable for site-to-site VPN configurations involving FortiSASE spokes.
* Configuration Adjustment:
* To establish the VPN tunnel, you need to disable mode config in the IPsec phase 1 settings.
* This adjustment will allow the FortiSASE spoke to properly establish the VPN tunnel with the FortiGate hub.
* Steps to Disable Mode Config:
* Access the VPN configuration on the FortiSASE spoke.
* Edit the IPsec phase 1 settings to disable mode config.
* Ensure other settings such as pre-shared key, remote gateway, and BGP configurations are correct and consistent with the FortiGate hub.
References:
FortiOS 7.6 Administration Guide: Provides details on configuring IPsec VPNs and mode config settings.
FortiSASE 23.2 Documentation: Explains the supported configurations for FortiSASE spoke devices and VPN setups.