The SD-WAN rule "Critical-DIA" (ID 1) is configured with set mode sla, which corresponds to the Lowest Cost (SLA) steering strategy. In this mode, FortiGate evaluates the interfaces defined in the priority-members list (1 then 2) in their specific order. It selects the first member in that list that currently meets the targets of the assigned Performance SLA (Corp_HC, SLA ID 1). The provided SD-WAN event log explicitly states that Member 1 (identified as port1 in the member status exhibit) has changed to "out-of-sla" for SLA Target ID 1. Consequently, FortiGate bypasses port1 and selects the next configured member in the priority list, which is Member 2 (port2), to steer the traffic.

A. FortiGate skips SD-WAN rule ID 1. FortiGate only skips a rule if the traffic packet does not match the rule's criteria; here, the rule is valid and has a secondary member available.

C. FortiGate uses port1 to steer the traffic for SD-WAN rule ID 1. The mode sla strategy requires the member to meet SLA targets; the event log confirms port1 is currently "out-of-sla," disqualifying it as the primary choice.

D. FortiGate uses port1 or port2 to steer the traffic for SD-WAN rule ID 1. The "Lowest Cost (SLA)" strategy is not a load-balancing mode; it follows a strict priority sequence and selects only one compliant member at a time.

Fortinet Documentation Library. FortiOS 7.4.0 Administration Guide: SD-WAN rules. Section: "Lowest cost (SLA) strategy".

Fortinet Training Institute. NSE 7 Network Security Architect: SD-WAN 7.2 Study Guide. pp. 108-114. (Detailed explanation of SLA-based member selection and priority-member ordering).