An administrator is troubleshooting SD-WAN on FortiGate.

According to theSD-WAN 7.6 Core Administratorcurriculum and the diagnostic outputs shown in the exhibit, the reason traffic is steered toHUB1-VPN3instead of the expectedHUB1-VPN1(defined in SD-WAN rule ID 1) can be explained by two core routing principles in FortiOS:

Valid Route Requirement (Option A): In thediagnose sys sdwan service 4output (which corresponds to Rule ID 1), it shows the rule has membersHUB1-VPN1,HUB1-VPN2, andHUB1-VPN3. A key principle of SD-WAN steering is that for a member to be "selectable" by a rule, itmust have a valid route to the destinationin the routing table (RIB/FIB). If the routing table output (the third section of the exhibit) shows a route to 10.0.0.0/8 viaHUB1-VPN3butnotthroughHUB1-VPN1, the SD-WAN engine will skip HUB1-VPN1 entirely because it is considered a "non-reachable" path for that specific destination.

Policy Route Precedence (Option D): In the FortiOS route lookup hierarchy,Regular Policy Routes (PBR)are evaluatedbeforeSD-WAN rules. If an administrator has configured a traditional Policy Route (found underNetwork > Policy Routes) that matches traffic destined for 10.0.0.0/8 and specifiesHUB1-VPN3as the outgoing interface, the FortiGate will forward the packet based on that policy route and willnever evaluate the SD-WAN rulesfor that session. This "bypass" occurs regardless of whether the SD-WAN rule would have chosen a "better" link.

Why other options are incorrect:

Option B: While member configuration priority (cfg_order) is a tie-breaker in some strategies, the SD-WAN rule logic is only applied if the routing table allows it or if a higher-priority policy route doesn't intercept the traffic first.

Option C: Lower route priority (which means higher preference in the RIB) affects theImplicit Rule(standard routing). However, SD-WAN rules are designed tooverrideRIB priority for matching traffic. If HUB1-VPN1 was a valid candidate and no Policy Route existed, the SD-WAN rule would typically ignore RIB priority to enforce its own steering strategy.