Legit FCSS_NST_SE-7.6 Exam Download

Based on the Fortinet FCSS - Network Security 7.6 documents and the analysis of the VPN tunnel exhibit, here is the verified answer.

Questions no: 91

Verified Answer: A, C

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

To determine the status of the VPN tunnel, we must examine the specific counters and fields in the diagnose vpn tunnel list output provided in the exhibit.

Analyze Phase 2 Status (Option A):

The output displays child_num=0.

In IKEv2 (and IKEv1 implementations in FortiOS), " Child SAs " refer to the Phase 2 (IPsec) Security Associations that carry the actual data traffic.

A value of 0 indicates that no Phase 2 tunnels are established. If Phase 2 were up, child_num would be at least 1.

Additionally, under the proxyid section, the field sa=0 confirms there is no active Security Association for that traffic selector.

Analyze Traffic Status (Option C):

The stat line shows: rxp=0 txp=0 rxb=0 txb=0.

rxp (Received Packets) and txp (Transmitted Packets) are both zero. This definitively confirms that no traffic is traversing the tunnel currently. This is expected since Phase 2 is down.

Analyze Phase 1 Status (Why B is incorrect):

The tunnel entry exists in the list with a valid tun_id, and NAT-Traversal is active (natt: mode=keepalive).

The presence of the tunnel in this command output, along with active Keepalive mechanisms, typically indicates that Phase 1 (IKE SA) is established and the peers are communicating on port 4500 (NAT-T), even though the data tunnels (Phase 2) failed to negotiate. If Phase 1 were down, the tunnel would often not appear in this " list " view or would show different status flags indicating a complete connection failure.

Conclusion: The exhibit shows a scenario where the Phase 1 control channel is likely up (evidenced by the entry existence and NATT keepalives), but the Phase 2 data channel is down (child_num=0), resulting in zero traffic flow (rxp=0/txp=0).

The session output includes the flags:

state=redir local may_dirty ...

npu_state=00000000

offload=0/0

The 7.6 study guide explains these flags directly:

local = “Session is to/from local stack”

redir = “Session is being processed by an application layer proxy”

may_dirty = “Session is allowed by a firewall policy”

This makes C correct, because the local flag means the session either originates from FortiGate or terminates on FortiGate . The FortiOS administration guide states the same meaning: “Session is originated from or destined for local stack.”

This also makes A correct. The redir flag means the session is handled by an application-layer proxy . FortiOS documents explain that proxy-based inspection buffers traffic on the FortiGate and inspects it there, and that proxy-based processing is CPU and memory-intensive

Since the session also shows no NPU offload (npu_state=00000000, offload=0/0), this traffic is being handled in software/CPU, not by the NPU.

Why the other options are wrong:

B is wrong because the redir flag proves the session is not passing without inspection; it is being processed by an application-layer proxy

D is wrong because there is no authentication flag in this session. In Fortinet examples of captive portal/authentication-related sessions, the session state includes auth or authed flags. The study guide shows: “Any session for traffic coming from an authenticated user contains the authed flag.” This exhibit does not show auth or authed, so there is no basis to conclude the client was redirected to a captive portal for authentication.

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.

To display debug output on FortiGate devices, you must always run both the application-specific debug command and the global debug enable command. The command diagnose debug application ike -1 sets up the detail level for the IKE daemon debug, but it does not display any debug output on its own. As described in the FortiOS CLI debugging manuals, the command diagnose debug enable activates debug output on the console, making all previously set debugs visible. This is especially important for VPN troubleshooting—without the enable command, no output appears even if there is VPN traffic.

The correct diagnostic sequence is:

diagnose debug application ike -1

diagnose debug enable

This procedure is found in every FortiOS CLI debug tutorial and troubleshooting workflow.