Fortinet Updated FCSS_NST_SE-7.6 Exam Questions and Answers by haleema

To determine the correct reasons for the adjacency failure, we must analyze the standard OSPF real-time debug output (diagnose ip router ospf all enable or diagnose sniffer packet) typically provided in this exam exhibit.

Analyze the Debug Output:

The debug output in this specific question scenario typically displays an incoming Hello packet line: OSPF: RECV[Hello]: ... auth-type 0 ...

"RECV": Indicates the packet is coming from the Remote peer.

"auth-type 0": Indicates the Remote peer is sending "Null" (No) authentication.

Analyze the Failure:

The adjacency fails because the Local FortiGate is rejecting this packet.

If the Local FortiGate accepts "No Authentication", it would match auth-type 0 and form the adjacency.

Since it is failing (and producing a debug log), the Local FortiGate must be expecting a different authentication type (Type 1 Cleartext or Type 2 MD5).

Evaluate the Options:

A. The remote peer has either OSPF cleartext or MD5 authentication configured.

Incorrect. The debug shows auth-type 0 (No Auth) coming from the remote peer.

B. There is an OSPF authentication configuration mismatch.

Correct. One side is sending "No Auth" (Remote), and the other expects "Auth" (Local). This is a definition of a mismatch.

C. The local FortiGate does not have OSPF authentication configured.

Incorrect. If the Local unit had "No Auth" configured, it would match the Remote's auth-type 0, and the adjacency would come up. The failure implies the Local unit does have auth configured.

D. The local FortiGate has either OSPF cleartext or MD5 authentication configured.

Correct. Because the Local unit is rejecting the "No Auth" packet from the remote peer, it confirms that the Local unit has authentication enabled (expecting Type 1 or 2).

Conclusion: The breakdown of the OSPF negotiation shows that the Remote peer is sending no authentication (Type 0), while the Local FortiGate expects authentication, resulting in a mismatch.

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.

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.

Based on the Fortinet FCSS - Network Security 7.6 documents and the analysis of the provided exhibits, here are the verified answers.

Questions no: 93

Verified Answer: B

Comprehensive and Detailed Explanation with all FCSS - Network Security 7.6 documents:

To determine which IP address was resolved via DNS, we must interpret the Flags column in the diagnose debug rating output provided in the exhibit:

Analyze the Flags:

Flag I (Initial): This flag indicates the IP address that was returned by the DNS query when resolving the FortiGuard FQDN (e.g., service.fortiguard.net). It acts as the "seed" or initial contact point.

Flag D (Discovered): This flag indicates servers that were not resolved via DNS but were learned dynamically from the FortiGuard network during protocol exchanges (server lists sent by the initial server).

Flag F (Failed): Indicates a server that the FortiGate tried to contact but failed.

Examine the Exhibit:

The IP address 209.22.147.36 has the flag I next to it.

The IP 208.91.112.194 has the flag D.

The IP 121.111.236.179 has the flag F.

Conclusion:

Since the question asks specifically for the IP obtained when resolving the name, we look for the "Initial" (I) flag. Therefore, 209.22.147.36 is the correct answer.