An administrator configures the performance service-level agreement (SLA) with the probe mode, Passive.

FortiGate supports Active, Passive, and Prefer Passive performance SLA monitoring modes. Passive monitoring measures actual network traffic rather than generating synthetic probes.

Option B is correct in the conventional preferred-link scenario because passive measurement depends on traffic traversing an SD-WAN member. When traffic is forwarded exclusively through the preferred link, FortiGate cannot measure the performance of unused alternative links. This is a limitation of passive monitoring.

Option D is correct because FortiGate uses TCP session information to measure latency, jitter, and packet loss. Latency measurements are derived from TCP connection behavior, while packet loss and jitter are determined using TCP header information.

Option A is incorrect because passive measurement relies on TCP session characteristics rather than ICMP traffic.

Option C is incorrect because enabling passive WAN health measurement disables automatic ASIC offloading on the affected firewall policies, allowing FortiGate to inspect the required TCP session information.

Option E is incorrect because the three-minute fallback to active probing belongs to Prefer Passive, not Passive mode. In Prefer Passive mode, FortiGate activates probes after three minutes without qualifying TCP traffic.