The output of the diagnose sys session list command provides the critical evidence needed to determine the behavior during a failover:
Session Synchronization (synced):
The most important indicator in the exhibit is the synced flag located in the state= line (state=may_dirty synced none app_ntf).
In FortiOS HA (High Availability), the synced flag confirms that this specific session has been successfully synchronized from the primary device to the secondary (backup) device.
Session synchronization (Session Pickup) ensures that if the primary unit fails, the secondary unit already has the session in its table and can resume traffic processing immediately.
TCP State (proto_state=01):
The output shows proto=6 (TCP) and proto_state=01.
In the FortiGate session table, proto_state=01 for TCP indicates that the session is in the ESTABLISHED state (post-three-way handshake).
This invalidates Option B, which claims the TCP session is not fully established.
Failover Outcome:
Because the session is ESTABLISHED and SYNCED, the secondary device will seamlessly take over the session upon primary failure.
The traffic continues to flow through the new primary without requiring the user/client to restart the connection. This is the primary function of HA Session Pickup.
Why other options are incorrect:
A: While the output shows app_ntf (Application Control notification) and may_dirty, the presence of the synced flag overrides this concern regarding failover. If the session type were not supported for failover (e.g., certain proxy sessions in older versions), it would not be marked as synced. Since it is synced, it persists.
B: As noted, proto_state=01 means established, not " not fully established " .
D: While the kernel updates routing tables, the purpose of syncing the session is to preserve the state so it does not need to be re-evaluated as a new packet would, preventing traffic drops.
Reference:
FortiGate Security 7.6 Study Guide (High Availability): " If session pickup is enabled, the primary unit synchronizes its session table... to the backup unit. If the primary unit fails, the backup unit... continues to process the sessions with no interruption. "

Analyze the " Send to Application Layer " Message:
The most critical line in the debug output is: id=65308 ... func=av_receive ... msg= " send to application layer
"
Meaning: This message indicates that the FortiGate kernel is handing the packet over to a user-space daemon (specifically the WAD/Proxy process, indicated by av_receive handlers) for deep inspection.
Implication: This behavior is the hallmark of Proxy-based inspection. In Flow-based inspection, the traffic is handled by the IPS engine (often within the kernel or via specific IPS handlers like ips_measure), and you would not typically see a " send to application layer " message for standard web filtering.
Evaluate Option B (Firewall Policy Mode):
Since the traffic is being sent to the application layer proxy, the Firewall Policy controlling this traffic (Policy ID 1, as seen in Allowed by Policy-1) must be configured with Inspection Mode = Proxy. If it were Flow- based, the traffic would stay in the flow path. Thus, Option B is correct.
Evaluate Option C (Web Filter Profile Mode):
In FortiOS, when a firewall policy is set to Proxy-based inspection, the security profiles (like Web Filter) applied to that policy also operate in Proxy-based inspection mode. The presence of the av_receive function confirms that the content inspection (Web Filter/AV) is being performed by the proxy engine. Thus, Option C is correct.
Why Option A is Incorrect (NPU Offload):
The output shows npu_state=0x100. In the context of a flow trace where traffic is being " sent to application layer, " this confirms the session is not fully offloaded to the NPU (Network Processor). Offloaded traffic (Fast Path) is handled by the hardware and would not generate these specific CPU-level debug logs for the payload inspection phase. The proxying process requires CPU intervention.
Why Option D is Incorrect (Port Mapping):
While valid protocol mapping is necessary for inspection, the specific debug output shown is a direct result of the Inspection Mode (Proxy vs. Flow). The observation of the traffic moving to the application layer is primarily caused by the policy and profile mode settings, making B and C the direct " observations " derived from the log data.
Reference:
FortiGate Troubleshooting (Debug Flow): " If the debug flow shows msg= ' send to application layer ' , it confirms the traffic is being handled by the proxy (WAD) for Proxy-based inspection. "

The correct answer is C. The session is offloaded using NPU .
The exact session example in the study guide shows:
* proto=6 # this is a TCP session
* expire=3599 # the session will expire in 3599 seconds , not in one second
* hook=post dir=org act=snat 10.9.31.117:45388- > 200.8.57.5:443(10.1.0.3:45388)
* hook=pre dir=reply act=dnat 200.8.57.5:443- > 10.1.0.3:45388(10.9.31.117:45388)
* npu info: ... offload=8/8 ...
* and the slide explicitly states: "Offloaded in both directions using NP6" The study guide also explains this exact point clearly:
"Counters for hardware acceleration-The presence of the npu info field indicates the session has been offloaded to hardware acceleration. In this example, traffic is being offloaded in both directions using network processor (NP) 6, which is represented by the value of 8." Why the other options are wrong:
* A is wrong because expire=3599, not 1. The duration=1 field means the session has existed for 1 second, not that it will expire in 1 second.
* B is wrong because the original session is from 10.9.31.117 to the remote server 200.8.57.5:443. The IP 10.1.0.3 is the SNAT-translated source address , not the final destination.
* D is not the best answer for this single-select question . The reply is indeed DNATed back toward the original client, but the exact validated takeaway highlighted by the study guide for this exhibit is the NPU offload state .

The correct answer is A.
The study guide explains the IKEv2 exchange order very clearly:
"The initial exchanges are: IKE_SA_INIT and IKE_AUTH."
"Create_Child_SA exchange: Creates a new child SA or rekeys an existing child SA." It also states:
"After successful IKE_SA_INIT and IKE_AUTH exchanges, the CHILD_SA exchange takes place. In this exchange, the peers negotiate the CHILD_SA and the traffic selectors - traffic selector responder (TSr) and traffic selector initiator (TSi)." That is why A is correct: if the tunnel was initially brought up successfully, then the initial exchanges already succeeded. A later problem during CREATE_CHILD_SA, especially with traffic selectors/phase 2 selectors, can cause the tunnel to fail during rekey or child-SA renegotiation.
Why the other options are wrong:
B is wrong because proposal mismatch for the IKE SA is handled during IKE_SA_INIT, not after the tunnel is already up. The study guide says IKE_SA_INIT negotiates the security settings to protect the IKE traffic C is wrong because a pre-shared key mismatch is part of authentication and would prevent successful initial establishment during IKE_AUTH. The study guide shows that after IKE_AUTH, "authentication succeeded" and "established IKE SA" when it works D is wrong because a Diffie-Hellman mismatch belongs to IKE_SA_INIT, which happens before the tunnel comes up. The study guide also states: "By IKEv2 design, no Diffie-Hellman public key is exchanged during an IKE_AUTH exchange." So the verified answer is: A.