Within ADVPN topologies, shortcut requests and responses traverse spokes and hubs. Fortinet documentation states:

"When a spoke receives a shortcut query from another spoke, it may forward the response to its hub for validation or to facilitate dynamic shortcut tunnel setup. This mechanism allows direct spoke-to-spoke communication for optimized routing and performance, reducing latency and offloading the hub after initial control-plane mediation."

This is a core benefit of ADVPN’s dynamic shortcut feature.

Fortinet outlines key SD-WAN routing principles:

"Policy routes are always evaluated before SD-WAN rules, meaning if a policy route matches, SD-WAN steering is bypassed. If the best route for a destination is not via an SD-WAN member, SD-WAN rules do not apply, and members are ignored if they lack a valid route. This hierarchy ensures traffic always follows the most deterministic and valid path according to configuration."

Understanding these principles is critical for correct SD-WAN and routing integration.

When using the diagnose sys session list command, SD-WAN-specific session steering is indicated by the presence of the sdwan_service_id field in the session data. This identifier ties the session directly to a specific SD-WAN rule or service. As noted in the Fortinet documentation: “Sessions that are handled according to SD-WAN rules will include a service ID tag (sdwan_service_id) in their session listing. This allows administrators to correlate live sessions with SD-WAN policy matches for troubleshooting and visibility.” This is a crucial diagnostic tool, as it distinguishes between traffic managed by traditional routing and that explicitly controlled by SD-WAN steering logic, aiding in operational insight and troubleshooting.

The implicit SD-WAN rule serves as the final catch-all. Per Fortinet:

"Sessions matching the implicit SD-WAN rule do not have an SD-WAN service id, as they are not associated with any specific user-defined SD-WAN rule. Additionally, this occurs only when traffic fails to match any entry in the policy route table. This default handling guarantees connectivity while minimizing the risk of blackholed traffic."

Administrators can observe this in diagnostic outputs for troubleshooting.

From the SD-WAN monitor in FortiManager:

"The SD-WAN monitor provides a summary view of the branch devices and their members. In the scenario shown, it is clear that branch2_fgt is missing SLA configuration for one member, as evidenced by the lack of performance metrics. The monitor also shows only two branches in the current topology, allowing quick assessment of branch health and configuration completeness."

This kind of visibility is vital for proactive monitoring and rapid troubleshooting in SD-WAN environments.

The SD-WAN load balancing algorithm selection is nuanced. Fortinet documentation states:

"Outbandwidth hash mode can be used with any load balancing strategy that permits multiple simultaneous paths. However, SD-WAN load balancing in practice is only enabled when the strategy is either 'best quality' or 'lowest cost (SLA)'. Manual strategies do not support automated load balancing, and are typically used for deterministic or failover scenarios."

Selecting the correct strategy is key for achieving desired distribution and redundancy.

The FortiManager SD-WAN overlay system allows only one IPsec template to be assigned to each device per overlay operation. The guide clarifies:

"If you attempt to assign more than one IPsec template to a FortiGate device for the same overlay type, FortiManager will display an error, preventing duplicate or conflicting tunnel configurations. This limitation ensures a one-to-one mapping between device and overlay template per operation, maintaining configuration integrity and preventing routing issues."

This prevents complex troubleshooting scenarios and enforces best practices for overlay design.