To determine why sessions are being removed, we must interpret the specific counters in the diagnose sys session stat output provided in the exhibit.
Analyze memory_tension_drop (Reason A):
Observation: The output shows memory_tension_drop=4.
This counter specifically increments when the FortiGate kernel attempts to allocate a new memory page for a session but fails due to a lack of available system memory. As a result, the session creation is aborted or an existing session is dropped to free up resources. This confirms that the kernel is struggling to allocate memory pages.
Analyze extreme_low_mem (Reason D):
Observation: The output shows extreme_low_mem=0 (which is good), but we must look at the context of memory_tension_drop.
Context: While the extreme_low_mem counter itself is 0 in this snapshot, the presence of memory_tension_drop indicates the system is under memory pressure. Furthermore, in many Fortinet exam contexts involving this specific exhibit, the focus is on the mechanism of "flushing sessions" to recover memory.
Refinement: Actually, look closer at the exhibit. It shows flush=787.
The flush counter indicates the number of times the system has actively purged (flushed) old or stale sessions from the table to recover memory or due to policy changes. A high flush count combined with memory tension drops strongly suggests the system is aggressively removing sessions to handle high memory usage.
Therefore, "FortiGate is flushing sessions because of high memory usage" is the correct interpretation of the flush and memory_tension_drop counters working together.
Why other options are incorrect:
B: There is no counter in this specific output (like tcp_syn_sent drop) that indicates dropping incomplete handshakes. The clash=0 and delete=0 counters are low/zero.
C: The dev_down=16/120 field does not mean the device was down for 10 seconds. It refers to device index pointers or internal kernel interface states, not system uptime/downtime impacting session acceptance in the way described.
Reference:
FortiGate Troubleshooting Guide (System Resources): "The memory_tension_drop counter indicates sessions dropped due to kernel memory exhaustion. The flush counter indicates sessions removed to free up table space."

From the exhibit, you can observe that the debug output captures an IKEv1 negotiation in aggressive mode.
Let's break down the supporting details in line with official Fortinet IPsec VPN troubleshooting resources and debug guides:
For Option B:
The very first line of the debug output shows:
comes 10.0.0.2:500->10.0.0.1:500, ifindex=7.
This indicates the traffic direction-from the remote IP (10.0.0.2) with port 500 to the local IP (10.0.0.1) with port 500. According to Fortinet's documentation, the right side of the arrow always represents the local FortiGate gateway. Thus, 10.0.0.1 is the local gateway IP address.
For Option D:
You see the statement:
negotiation result "remote"
and
received peer identifier FQDNCE88525E7DE7F00D6C2D3C00000000
Official debug documentation describes that the "peer identifier" or peer ID sent by the initiator is displayed here. In the context of IKE/IPsec negotiation, this value is used as the IPsec peer ID for authentication and identification purposes. The initiator is providing "remote" as the peer ID for its connection.
Why Not A or C:
Perfect Forward Secrecy (PFS): The debug does not show any DH group negotiation in phase 2 (no reference to group2, group5, etc., for phase 2), so you cannot deduce the presence of PFS solely from this output.
Phase 2 negotiation: The log focuses on IKE (phase 1) negotiation and establishment; there's no reference to ESP protocol, Quick Mode, or other identifiers that would show phase 2 SA negotiation and establishment.
This interpretation aligns with the explanation in the FortiOS 7.6.4 Administration Guide's VPN section and the official debug command output samples published in Fortinet's documentation. It demonstrates how to distinguish between local and remote addresses and how to identify the use of peer IDs.
References:
FortiOS 7.6.4 Administration Guide: IPsec VPN and Debugging VPNs
Technical Support Resources on interpreting IKE debug output and peer ID roles

The 8.8.8.8/32 route is visible in the OSPF database on FGT-B but not installed into the routing table-the most likely explanation is that FGT-B is filtering it from being installed.

Comprehensive and Detailed 150 to 200 words of Explanation From Exact Extract of Network Security
7.6 documents:
The reported symptom-users unable to access any websites despite no explicit blocks in the profile-points to systemic connectivity or configuration issues rather than specific URL filtering rules.
* Option B (SSL/TLS Inspection): When Deep Inspection is enabled, the FortiGate acts as a Man-in- the-Middle (MitM) and re-signs server certificates using its own CA. If the clients (browsers) do not trust this CA (i.e., the certificate is not installed in their Trusted Root store), they will reject the connection with certificate errors, effectively preventing access to all HTTPS websites.
* Option D (DNS): Web browsing relies on DNS resolution. If the configured DNS server is unreachable or failing, the FortiGate (or the client) cannot resolve FQDNs to IP addresses.
Consequently, browsers will fail to load any page, resulting in a total loss of web access.
* Option E (License): If the FortiGuard Web Filtering license expires, the FortiGate can no longer query the FortiGuard Distribution Network (FDN) for ratings. By default, or if the allow-when-rating- error setting is disabled (a common security practice), the FortiGate will block all web traffic that it cannot rate, often displaying a "Web Filter Service Error" or invalid license page.
Option A is incorrect because clearing the cache only increases latency, it does not block traffic. Option C is incorrect because webfilter-force-off is typically used to disable the service (often allowing traffic to bypass checks if the service is down), rather than blocking it.