The line sdwan_mbr_seq=1 sdwan_service_id=4 indicates that this session is part of an SD-WAN rule. sdwan_service_id=4 confirms that the session is being handled by SD-WAN rule ID 4. This directly links the flow to the SD-WAN configuration.

The line no_offload_reason: redir-to-ips denied-by-nturbo shows that the session is not offloaded to the NPU (Network Processing Unit) and is being processed by the main CPU. A session that is not offloaded can be re-evaluated. If the outgoing interface (the one currently being used) goes down, the FortiGate will re-evaluate the session against the SD-WAN rules to find a new active member to steer the traffic through. This is a fundamental behavior of SD-WAN, which ensures network resilience.

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.

Specify the gateway of the SD-WAN member port1 with an IP address or use the default value → The error log shows invalid ip – prop[gateway]: ip4class(${sdwan_port1_gw}) invalid ip addr, meaning the variable ${sdwan_port1_gw} does not have a valid mapping. Assigning a valid IP address or default value for the gateway resolves this error.

Review the per-device mapping configuration for metadata variables → The issue is tied to how the metadata variable ${sdwan_port1_gw} is mapped for branch1_fgt. If this device does not have the variable properly defined in per-device mapping, the configuration will fail. Correcting the mapping ensures that the install works.

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 FortiManager SD-WAN overlay template preview, as described in the document, indicates:

" When the device is acting as a hub, the configuration enables the sending of ADVPN shortcut offers to spokes. This means the hub can facilitate on-demand dynamic shortcut tunnel creation between spokes, improving performance for branch-to-branch communication by bypassing the hub for inter-branch traffic after initial discovery. "

Such a role is critical in scalable ADVPN topologies, enabling hub devices to optimize overlays dynamically.

The router policy explicitly denies traffic with source 10.0.1.128/25 (which includes 10.0.1.130) and destination 128.66.0.0/24 (which includes 128.66.0.125). Even though SD-WAN service 4 shows members (port1 and port2) alive and available for this traffic, the router policy is evaluated first and blocks it. Therefore, FortiGate drops the traffic flow.

When referencing a zone in a static route, FortiGate’s behavior is described as:

" Referencing a zone in a static route causes FortiGate to install a static route for each member interface of the zone. This enables ECMP (Equal-Cost Multi-Path) and load balancing where supported and ensures that traffic can be steered over any valid zone member according to SD-WAN rules or standard routing. "

This mechanism is fundamental to Fortinet’s implementation of SD-WAN and simplifies large, multi-interface deployments.