FCSS_NST_SE-7.6 Fortinet NSE 6 - Network Security 7.6 Support Engineer Questions and Answers

Intermittent behavior (working sometimes, failing others) points to resource or connectivity fluctuations rather than static misconfigurations.

B. Check that FortiGate is not entering conserve mode:

Reason: When FortiGate enters Conserve Mode (due to high memory usage), it changes its inspection behavior to save resources. Depending on the av-failopen setting, it may either bypass inspection (allowing blocked sites) or drop traffic (blocking valid sites) temporarily until memory recovers. This flapping between states causes intermittent filtering issues.

D. Check that the communication between FortiGate and FortiGuard is stable:

Reason: The Web Filter engine relies on real-time queries to the FortiGuard Distribution Network (FDN) to categorize URLs that are not in the local cache. If the internet connection or the specific path to FortiGuard is unstable (packet loss, latency), queries will time out. This results in "Rating Errors," which can block or allow traffic unpredictably based on the "Allow websites when a rating error occurs" setting.

Why other options are incorrect:

A: A mismatch in inspection mode (e.g., Profile set to Proxy, Policy set to Flow) is a static configuration error. It would typically result in the profile not being selectable or consistently failing/not applying, rather than working intermittently.

C: If the wrong port is mapped (e.g., HTTP on 8080 is not mapped), the inspection engine will consistently ignore traffic on that port. It would not be intermittent.

The BGP debug output shows session information for peers, including state details. According to official Fortinet BGP documentation, if the session state with a peer does not show "Idle," "Active," or "Connect," but instead shows "Established," "Up," or related counters (e.g., messages sent/received or uptime), it indicates the session is operational. In this scenario, the peer 10.127.0.75 is the only one showing a positive indication of a live, established session. Other options like neighbor-range configuration, AS mismatch, or route-maps blocking prefixes are not supported by evidence provided in a simple BGP session state debug, nor does the output show errors relating to local or remote AS issues.

The correct interpretation comes from Fortinet's BGP troubleshooting guide, which outlines how to read session status and neighbor states in debug and summary outputs.

According to the official Fortinet documentation (Technical Tip: Useful FSSO Commands), heartbeat messages play a crucial role in communication between the FSSO Collector Agent and FortiGate. These messages are regularly sent from the Collector Agent to verify its status, maintain session awareness, and confirm connectivity between the authentication infrastructure and FortiGate appliances.

Option B is confirmed by Fortinet, as the collector agent logs on Windows or its management console will specifically note heartbeat events, connection status, and any issues maintaining contact with FortiGate units.

Option C is validated by both official CLI documentation and the technical tip linked. On FortiGate, heartbeat messages from the collector agent are visible using real-time debug tools such as diagnose debug application authd or FSSO-specific commands. These enable administrators to monitor live logon states, session status, and connection health directly from the FortiGate CLI. The debug stream shows heartbeats received and their effect on active logons, associating health monitoring with active sessions.

Heartbeat operation is fully automated once FSSO is set up—there is no requirement for manual enablement or configuration, aligning with Fortinet’s philosophy of seamless integration and centralized management across the Security Fabric. This ensures that both FortiGate and the collector agent can quickly and reliably detect any miscommunication or outage, addressing authentication issues proactively.

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.

Comprehensive and Detailed 150 to 200 words of Explanation From Exact Extract of Network Security 7.6 documents:

The correct answer is A. This behavior is dictated by the configuration command set snat-route-change enable shown in Exhibit 1 under config system global.

Routing Change: By changing the priority of route ID 2 from 10 to 0, it becomes lower than route ID 1 (priority 5). In FortiOS, a lower priority value indicates a more preferred route. Consequently, the active route for the destination changes from port1 to port2.

SNAT Implication: The existing session (shown in Exhibit 2) is using Source NAT (SNAT) with the IP address associated with port1 (10.200.1.1). If the traffic were simply switched to port2, the source IP would be incorrect for that interface and the return traffic would likely fail or be dropped.

snat-route-change enable: This specific setting instructs the FortiGate on how to handle established SNAT sessions when a routing change occurs that alters the preferred outgoing interface. When enabled, if a route change forces an SNAT session to a new interface, FortiGate flushes (deletes) the session from the session table. This is necessary because a live TCP session cannot survive a change in its source IP address. The client must initiate a new session, which will then be created using the new correct route (port2) and the corresponding new SNAT IP.

If this setting were disabled, the session would likely remain "sticky" to the original interface (port1) until it closed, provided the route still existed. However, the explicit configuration forces the deletion.

Comprehensive and Detailed 150 to 200 words of Explanation From Exact Extract of Network Security 7.6 documents:

The get router info ospf database brief output on FGT-2 clearly indicates that Area 0.0.0.5 is configured as a [Stub] area.

In OSPF, a Stub Area is specifically designed to reduce the size of the Link State Database (LSDB) on internal routers. The primary behavior of a Stub area is that it does not accept Type 5 (AS External) LSAs.

FGT-3 is the ASBR (Autonomous System Border Router) and is importing static routes, which are generated as Type 5 LSAs in the OSPF domain.

FGT-1 acts as the ABR (Area Border Router). Because Area 0.0.0.5 is a Stub area, FGT-1 blocks these Type 5 LSAs from entering Area 0.0.0.5.

Consequently, FGT-2 will not receive the specific external routes advertised by FGT-3. Instead, the ABR (FGT-1) injects a default route (0.0.0.0/0) into the Stub area to allow connectivity to the external world, which is visible in the database output.

While the question text mentions FGT-3 not receiving routes, the definitive configuration shown in the exhibit is the Stub area setting, which directly corresponds to the blocking of Type 5 LSA propagation (Option A).

To establish a functional Security Fabric, specific network and configuration prerequisites must be met to ensure nodes can communicate, authorize, and share telemetry data:

A. You must ensure that TCP port 8013 is not blocked along the way:

TCP port 8013 is the dedicated port for FortiTelemetry (Fabric) communication. If firewalls (intermediate or local) block this port, the Fabric connection between the root and downstream FortiGates will fail.

D. You must authorize the downstream FortiGate on the root FortiGate:

Security Fabric relies on a trust relationship. When a downstream device attempts to join, it appears in the Root FortiGate's dashboard. The administrator must manually authorize this device (unless pre-authorized via serial number) to allow it to join the Fabric topology.

E. You must enable FortiTelemetry on the receiving interface of the upstream FortiGate:

The interface on the Root (upstream) FortiGate that faces the downstream devices must have the "Security Fabric Connection" (formerly CAPWAP/FortiTelemetry) administrative access setting enabled. Without this, the interface will not listen for or accept Fabric connection requests.

Why other options are incorrect:

B: Neighbor Discovery uses standard multicast/broadcast or static settings; changing the port is not a standard requirement.

C: FortiGates can participate in the Security Fabric in either NAT or Transparent mode; Transparent mode is not a mandatory requirement for the Fabric itself.

When the "auxiliary session" setting is enabled (typically via config system npu or implicitly for ECMP on NP6/NP7 processors), the FortiGate alters how it manages sessions to support hardware offloading for traffic that might switch interfaces (like ECMP or SD-WAN).

B. FortiGate accelerates all ECMP traffic to the NP6 processor:

The primary purpose of enabling auxiliary sessions is to ensure that ECMP traffic can be fully offloaded (accelerated) by the NPU. Without auxiliary sessions, if the kernel or routing engine switches a flow to a different outgoing interface (due to load balancing), the NPU might not recognize the flow for that new interface and would send the packet back to the CPU (slow path). Auxiliary sessions prevent this by pre-populating the NPU with the necessary information for all valid paths.

D. FortiGate creates two sessions in case of a routing change:

Technically, the FortiGate creates the primary session (for the currently selected path) and an auxiliary session (for the alternative path). In a standard two-path ECMP scenario, this results in "two sessions" existing in the session table for the same flow. This ensures that if a routing change occurs (e.g., the flow shifts to the second path), the traffic continues to be processed by the NPU without interruption or re-evaluation by the CPU.

FortiGate HA Troubleshooting and Synchronization Guides

Fortinet Admin Guide: HA Primary Role Retention, Cluster Break-up Due to Out-of-Sync Status

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.

According to RFC 7296 (IKEv2) and Fortinet's official documentation, the IKE_SA_INIT exchange is responsible for negotiating cryptographic parameters, performing the initial Diffie-Hellman exchange, and implementing the cookie challenge mechanism for DoS protection. When the responder suspects a DoS attack (such as mass requests by the same source), it includes a cookie in the IKE_SA_INIT response. The initiator must return the cookie in its next request to prove that it truly exists at the IP address it claims, thereby mitigating resource exhaustion attacks.

This two-step exchange ensures the responder only allocates resources after successful proof of address, aligning with best security practices. Fortinet documentation confirms that this process occurs strictly in the IKE_SA_INIT phase, not in subsequent IKE_Auth or CHILD_SA exchanges.

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Using-the-diagnose-sys-top-CLI-command/ta-p/190238

The IKE_SA_INIT exchange in IKEv2 is responsible for DoS protection measures. During IKE_SA_INIT, before authentication and further exchange, the responder can use cookie challenges (per RFC 7296 and Fortinet VPN documentation). If a DoS attack is suspected (many requests from the same source), the responder replies with a cookie. Only after the initiator returns the correct cookie does the exchange proceed, protecting the responder from state exhaustion and certain forms of DoS traffic at the handshake stage.

To determine the cause of the failure, we must analyze the IKEv2 debug output provided in the exhibit (image_ad3dc6.jpg):

Identify the Negotiation Phase:

The debug log shows: responder received CREATE_CHILD exchange.

In IKEv2, the CREATE_CHILD_SA exchange is used to create new Child SAs (Phase 2) or to rekey existing ones.

The fact that the tunnel was previously "brought up successfully" implies the initial IKE SA (Phase 1) is stable, and this error is occurring specifically during a rekey event, which often involves Perfect Forward Secrecy (PFS).

Analyze the Proposals (The Mismatch):

Incoming Proposal (Remote Peer):

The remote peer sends a proposal containing two Diffie-Hellman groups: type=DH_GROUP, val=MODP2048 (Group 14) and type=DH_GROUP, val=MODP1536 (Group 5).

My Proposal (Local FortiGate):

The local FortiGate configuration expects: type=DH_GROUP, val=MODP3072 (Group 15).

Result of the Negotiation:

The debug output concludes with: no proposal chosen and Negotiate SA Error.

This error occurs because the local FortiGate cannot find a common Diffie-Hellman group between what it requires (Group 15) and what the peer is offering (Groups 14 or 5).

While this is technically a mismatch occurring during the Phase 2 (Child SA) creation, "A Diffie-Hellman mismatch" (Option A) is the precise root cause identified in the logs.

Why other options are incorrect:

B: The log shows received create-child request, confirming that UDP traffic is reaching the device and is not blocked.

C: The failure is in the CREATE_CHILD exchange (Phase 2/Rekey), not the IKE_SA_INIT or IKE_AUTH (Phase 1) exchanges.

D: While the mismatch is occurring within the Phase 2 definitions, Option A is the specific technical reason for the no proposal chosen error shown in the DH_GROUP lines.

The diagnose debug authd fsso server command is the primary tool for troubleshooting communication between the FortiGate and the FSSO Collector Agent. This debug output reveals the status of the connection and the reasons for failure. The three most common connectivity issues identified by this debug are:

FortiGate cannot reach the IP address of the collector agent (Option C): The debug will show connection timeouts or "host unreachable" errors if the Layer 3 connectivity is missing.

The connection was refused / Port mismatch (Option B): If the FortiGate can reach the IP but the Collector Agent is not listening on the specified port (default 8000), the debug will display "Connection refused." This often happens if the port configured on the FortiGate does not match the listening port on the agent.

The pre-shared key does not match (Option D): If the IP and Port are correct, the next step is authentication. If the password configured on the FortiGate does not match the one on the Collector Agent, the debug will explicitly show an "Authentication failed" or "password mismatch" error during the handshake.

Note on other options: Option A (SSL) is less common than basic connectivity/auth mismatches. Option E (Group filters) relates to user processing logic, which occurs after connectivity is established.