To determine the behavior, we must analyze the memory thresholds and the current status shown in the exhibit:

Analyze the Thresholds (The Three States):

Green (Exit): 82% (Memory usage is safe).

Red (Enter Conserve Mode): 88% (Memory usage is high; action is required).

Extreme (Kernel Conserve Mode): 95% (Memory is critical; drastic action is required).

Determine the Current State:

Current Memory Used: 89%.

Since 89% is greater than the Red threshold (88%) but lower than the Extreme threshold (95%), the FortiGate is in Red Conserve Mode (User-space conserve mode), not Extreme mode.

Evaluate the Behavior in "Red" Mode:

In Red Conserve Mode, the FortiGate's primary goal is to prevent memory exhaustion while still processing traffic if possible.

Proxy-based inspection (handled by the WAD process) is memory-intensive because it buffers content. To save memory, the system stops accepting new sessions that require proxy-based inspection.

Flow-based inspection (handled by the IPS engine) streams data and consumes significantly less memory. Therefore, in Red mode, the system typically continues to allow and inspect flow-based sessions.

Option A correctly describes this split behavior: allowing flow-based (lighter) but blocking proxy-based (heavier).

Why other options are incorrect:

B: If memory increases another 6% (89% + 6% = 95%), the device hits the Extreme threshold. At 95%, the kernel begins dropping all new sessions to prevent a system crash. Thus, it will not continue to allow sessions.

C: This describes "Fail-Open" behavior (passing traffic without inspection). While configurable (set av-failopen pass), the default is usually "Fail-Close" (blocking). More importantly, the distinction between flow and proxy availability is the key architectural feature of Red mode.

D: Blocking all new sessions regardless of type is the behavior of Extreme Conserve Mode (95%). Since the device is only at 89%, this drastic measure is not yet active.