FCSS_NST_SE-7.6 Exam Dumps - Fortinet NSE 6 - Network Security 7.6 Support Engineer

To determine the path the traffic will take, we must look at the FortiGate Route Lookup Precedence (Packet Processing Flow) and the specific configurations shown in the exhibit

Analyze the Routing Precedence:

In FortiOS, when a packet arrives (and is not part of an existing session), the FortiGate performs route lookups in a specific order:

Policy Routes: Configured under config router policy (or diagnose firewall proute list). These are checked first. If a packet matches the criteria (Source, Destination, Protocol, Incoming Interface), the Policy Route is used immediately, bypassing the standard routing table.

FIB (Forwarding Information Base): If no Policy Route matches, the device looks at the standard routing table (Static, Connected, Dynamic).

Analyze the Exhibit:

Policy Route Section: The output of diagnose firewall proute list shows an active policy route (id=1).

Destination: 100.65.0.0/255.255.255.0 (Matches the network in the question).

Action: It directs traffic to gateway 10.0.4.253 via oif=6(port4).

Routing Table Section: The output of get router info routing-table database shows multiple routes for 100.65.0.0/24 (Static, OSPF, BGP) all with distance 10. The Static route (S) is currently selected (*>) in the FIB.

Conclusion:

Because Policy Routes take precedence over the standard routing table (FIB), the FortiGate will forward the traffic using the instructions in Policy Route ID 1. It will not use the Static, BGP, or OSPF routes visible in the routing table for any traffic that matches the policy route's criteria (ingress port 3).

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.

FortiOS Admin Guide: Static Routing, SNAT Route Change Feature

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.

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.

**

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.

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.