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Comprehensive and Detailed 150 to 200 words of Explanation From Exact Extract of SD-WAN 7.6 Enterprise Administrator documents:

When a FortiGate device is onboarded using a Device Blueprint in FortiManager, the system automates the provisioning process by applying the linked templates and scripts as soon as the device is authorized and connects. In this scenario, the Device Blueprint includes a CLI Template named "LAN-interface" and Provisioning Templates (corp_st and LAN-interface).

According to Fortinet documentation regarding Zero-Touch Provisioning (ZTP) and Blueprint workflows, FortiManager processes the CLI script configuration as part of the initial onboarding sync. The provided CLI script explicitly contains instructions for port1, port2, and port5. Specifically, it sets port1 and port2 to mode dhcp. Even though port1 already has a manual IP address ($15.1.0.154$) used for the initial FGFM connection, the FortiManager will push the configuration defined in the template.

When FortiManager pushes a configuration change to the interface used for the FGFM tunnel (port1), it does so by updating the configuration database. Since the template specifies set mode dhcp for port1 and port2, and a specific IP range for port5 using a metadata variable (10.0.$(branch_id).254), all three ports will be updated. Consequently, they may receive new IP addresses based on DHCP assignments or variable substitution. FortiManager is capable of updating the management interface as long as the new configuration does not permanently sever the FGFM connection.

When the member priority of a port is increased (e.g., port2 to 20), FortiGate evaluates existing sessions and applies “dirty” flags where applicable. The SD-WAN session management mechanism is described in detail: “Upon a change in SD-WAN member priority, all existing sessions using that member are marked as dirty. For SNAT sessions, the gateway information is updated to ensure future packets are routed through the newly preferred member, in this case, port1. This automatic re-evaluation allows SD-WAN to dynamically respond to topology or priority changes, maintaining optimal routing.” This is fundamental to seamless failover and session persistence in Fortinet SD-WAN, ensuring active flows are redirected based on updated priorities or health status.

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.

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.

To allow spokes in different hub-and-spoke groups to establish ADVPN shortcuts, the hubs must be configured to forward and send ADVPN shortcut offers. The key required settings on the hub are auto-discovery-forwarder (for VPNs to hubs) and auto-discovery-sender (for VPNs to spokes). This ensures the hub can facilitate and advertise ADVPN shortcut offers between spokes.

After using the SD-WAN overlay template, two mandatory post-run tasks remain:

"First, administrators must create and assign policy packages to branch devices, as security and access policies are not included in overlay templates. Second, SD-WAN rules must be configured so that traffic can be matched and steered appropriately through the established overlays. Neglecting either task results in ungoverned traffic or inefficient routing, undermining the benefits of SD-WAN."

Templates automate topology, but policy and rule definition are critical for operational effectiveness.

By default, local-out traffic does not use SD-WAN → FortiGate normally sends local-out traffic (e.g., DNS, NTP, FortiGuard updates) directly through its interfaces without applying SD-WAN rules.

You must configure each local-out feature individually to use SD-WAN → To steer local-out traffic via SD-WAN, you must explicitly configure the desired local-out features (e.g., DNS, FortiGuard, CAPWAP) to use SD-WAN rules.