Free Fortinet FCSS_NST_SE-7.6 Practice Exam with Questions & Answers | Set: 2

To capture encrypted IPsec phase 2 (ESP) traffic between two FortiGate devices, the correct protocol filter to use is ip proto 50. According to the Fortinet official sniffing and debugging documentation, ESP (Encapsulating Security Payload) is used for encrypted phase 2 payload transfer and always uses IP protocol number 50. Running the command diagnose sniffer packet any 'ip proto 50' captures only ESP packets, which represent the encrypted traffic—whether originating or transiting the device.

If there is no NAT device between FortiGates, ESP is not encapsulated in UDP (thus not on UDP port 4500; if NAT-T were required, packets would be UDP-encapsulated, but the scenario explicitly says NAT is not in use). UDP port 500 is for IKE control (negotiation) traffic, and AH (Authentication Header, ip proto 51) is not used for encryption in standard IPsec phase 2 with ESP.

This matches the official CLI reference from Fortinet for VPN and traffic analysis.

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To determine the correct conclusions, we analyze the specific lines in the IKE real-time debug output provided in the exhibit:

Analysis for Option A (The remote peer is the initiating peer):

Evidence: The very first line of the debug output reads: ike 0:624000:98: responder: main mode get 1st message...

The keyword responder indicates that this local FortiGate is receiving the connection request. Consequently, the remote peer must be the initiator sending the request. The phrase "get 1st message" confirms the local unit is receiving the initial packet of the negotiation sequence.

Conclusion: This statement is True.

Analysis for Option B (This is a phase 1 negotiation):

Evidence: The same line mentions main mode.

In IPsec VPNs, Main Mode and Aggressive Mode are exclusively used for Phase 1 (IKE SA) negotiations. Phase 2 (Child SA) negotiations use Quick Mode. The presence of "main mode" definitively identifies this as a Phase 1 exchange.

Conclusion: This statement is True.

Analysis for Option C (There is a Diffie-Hellman group mismatch):

Evidence:

Incoming proposal (Remote): Lists type=OAKLEY_GROUP, val=MODP2048 (Group 14) in the first proposal proposal.

My proposal (Local): Lists type=OAKLEY_GROUP, val=MODP2048 (Group 14).

Since both the remote peer and the local gateway support and are proposing MODP2048 (Group 14), there is no Diffie-Hellman group mismatch. The actual mismatch visible in the logs is between the Encryption/Hash algorithms (Remote proposes AES-256/SHA2-256, while Local proposes AES-128/SHA), but the DH groups match.

Conclusion: This statement is False.

Analysis for Option D (This is a phase 2 negotiation):

As established in the analysis for Option B, "Main Mode" is a Phase 1 protocol. If this were Phase 2, the debug would show "Quick Mode".

Conclusion: This statement is False.

The exhibit for question 4 shows a policy route table entry, and key fields are as follows:

internet service(1) : Fortinet-FortiGuard(1245324,0.0.0.0,0.0.0.0)

According to the Fortinet official documentation, when a policy route is based on Internet Service Database (ISDB) entries, the route entry will specifically mention “internet service,” showing the service being referenced (in this example, Fortinet-FortiGuard). This is fundamentally different from a regular policy route, which is defined by source, destination, and service wildcards without referencing an ISDB signature. A regular policy route's output would not contain the line “internet service.”

Policy routes that use ISDB allow FortiGate to steer traffic for specific well-known services (like FortiGuard, Google, Microsoft) based on traffic pattern recognition, even if the destination IP is dynamic. The matching and route selection follow the ISDB tag and can coexist with static or regular policy routes.

Thus, this entry is correctly and uniquely an ISDB route, as explained in the FortiOS policy routing documentation and ISDB configuration references.

IKEv1 (Internet Key Exchange version 1) and IKEv2 are protocols used for establishing IPsec VPN tunnels, and both protocols share the conceptual division into two phases, as clearly described in Fortinet VPN documentation:

Phase 1 handles negotiation and establishment of a secure IKE Security Association (SA) between peers.

Phase 2 negotiates parameters for the IPsec Security Association, which secures actual data traffic between peers.

While IKEv2 streamlines and improves upon IKEv1 by merging some message exchanges and simplifying configuration, it maintains the same core two-phase concept: Phase 1 (IKE SA) and Phase 2 (IPsec SA). This is a foundational VPN concept referenced widely in both IKEv1 and IKEv2 literature.

Other statements are incorrect:

Asymmetric authentication is possible, but not mandatory for both.

Both protocols commonly use UDP port 500, sometimes 4500 for NAT traversal, but they are not designed to run on TCP.

The protocol feature compatibility over TCP/UDP is not correctly described in the other options.

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.