Exam NSE6_SDW_AD-7.6 Topic 1 Question 77 Discussion

In FortiOS (including FortiOS 7.6), FortiGate follows a strict and well-defined route lookup order when determining how to forward traffic. This order is critical for understanding SD-WAN behavior and is explicitly referenced in the FCSS SD-WAN curriculum.
The correct lookup sequence is:
* Policy routes (Policy-Based Routing)Policy routes are evaluated first. If traffic matches a policy route, FortiGate immediately forwards the traffic according to that policy and bypasses all other routing mechanisms.
* Internet Service Database (ISDB) routesIf no policy route matches, FortiGate checks ISDB routes.
These routes match traffic based on Internet Services rather than destination IP prefixes.
* SD-WAN rulesIf neither a policy route nor an ISDB route matches, FortiGate evaluates SD-WAN rules to determine the outgoing interface based on the configured SD-WAN strategy.
* Routing table (connected, static, and dynamic routes such as BGP)If no SD-WAN rule matches, FortiGate performs a normal routing table lookup.
* FIB (Forwarding Information Base)The FIB is used to forward the packet based on the selected route.
* DropIf no valid route exists, the packet is dropped.
Among the options provided, only Option D correctly reflects the beginning of this sequence by placing policy routes first, followed by ISDB routes, then SD-WAN rules, and finally static routes (representing the routing table).
Therefore, the correct answer is D.