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

The issue is caused by the strict matching logic of the configured Prefix List.

Current State: The rule is edit 1 with set prefix 172.16.0.0 255.255.0.0 and both ge (greater than or equal) and le (less than or equal) are unset.

Behavior: When ge and le are unset, FortiOS requires an exact match of the subnet mask. The current rule only matches the exact network 172.16.0.0/16. It denies 172.16.52.0/24 because the mask (/24) does not match the rule ' s mask (/16).

To fix this and inject 172.16.52.0/24, you must modify the list to match the /24 mask:

A. Add another entry to the prefix list to specifically allow the 172.16.52.0/24 network:

Creating a new rule (e.g., edit 2) with set prefix 172.16.52.0 255.255.255.0 will provide an exact match for the incoming route, allowing it to pass the distribute-list.

B. Change the ge value to 17:

By configuring set ge 17 on the existing rule (conceptually 172.16.0.0/16 ge 17), you change the logic from " exact match " to " range match " .

This configuration tells the router to match any prefix starting with 172.16.x.x that has a subnet mask length of 17 or greater.

Since the incoming route is a /24, and 24 is greater than 17, the route will match the prefix list and be accepted.

Why other options are incorrect:

C: The option text appears to read " Change the ... value to 16 " . If this refers to le 16, it would enforce the mask to be exactly /16 or less, which still excludes /24.

D: Changing the default behavior to implicit allow defeats the purpose of a filter (security control) and is not a standard configuration step for fixing a single missing route.

The administrator is running a packet sniffer with the filter ' udp port 500 or udp port 4500 or esp ' . The result is " no output, " even though the VPN is attempting to establish (failing).

A. The VPN is configured to use IKE over TCP:

Standard IPsec IKE negotiation uses UDP port 500 (IKE) and UDP port 4500 (NAT-T).

However, if IKEv2 over TCP (RFC 8229) or Fortinet ' s proprietary IKE over TCP is configured (often used to bypass firewalls that block UDP), the traffic will use TCP (often port 4500 or 443).

The sniffer filter explicitly looks for udp or esp (IP Protocol 50).

If the traffic is encapsulated in TCP, it matches tcp protocol, not udp or esp (raw ESP). Therefore, the sniffer sees zero packets matching the filter.

Why other options are incorrect:

B: esp is a valid argument for diagnose sniffer packet. It is equivalent to filtering for IP protocol 50.

C: If the ISP were blocking traffic, the sniffer (running on the local FortiGate) would still see the outbound packets generated by the FortiGate trying to initiate the connection. " No output " implies the local device isn ' t even generating packets matching that filter.

D: Mismatched IKE versions would still generate IKE negotiation packets (proposals/errors) that would be captured by the sniffer.

The correct answers are A and B .

For UDP , the study guide states this directly: “For UDP, the session state can have only two values: 00 when traffic is only one way, and 01 when traffic is two ways. For ICMP, the protocol state is always 00.”

That makes B correct and D incorrect.

For TCP , the study guide explains that the protocol state is a two-digit number, where the first digit is the server-side state and the second digit is the client-side state . It also states that the first digit is 0 when the session is not subject to any inspection , and the TCP state table shows that value 1 = ESTABLISHED

So, for a normal non-proxied/non-inspected TCP session, proto_state=01 means the TCP session is in the ESTABLISHED state. An established TCP session means the three-way handshake has completed, which requires traffic in both directions. That is why A is correct.

The study guide also says: “proto_state=11 means that the TCP three-way handshake for both server-side and client-side is completed (ESTABLISHED).”

This confirms that TCP state value 1 represents an established state.

Why C is not selected: the study guide defines value 5 as TIME_WAIT and says: “When a session is closed by both the sender and receiver, FortiGate keeps that session in the session table for a few seconds… This is the state value 5.”

So proto_state=05 represents a closing/closed TCP session in TIME_WAIT , not the normal bidirectional state the question is testing.

Therefore, the verified answers are A and B .

The exhibit displays the output from the diagnose debug rating command on a FortiGate device. This command is used to display information about FortiGuard Web Filtering or other security-related queries performed by FortiGate to FortiGuard servers. Official Fortinet documentation outlines the meaning of each field in the server list. The FortiGate maintains a list of available FortiGuard servers, selecting the optimal server based on factors such as weight, round-trip time (RTT), and regional settings.

The very first entry in the server list after " Server List " is the server FortiGate initially uses, prioritized by factors such as proximity and RTT. Here, 64.26.151.37 is listed first, and the FortiGuard-requests value confirms that this server handled the highest number of requests.

The IPs, weights, and lost/failed counters are monitored for server performance and selection over time. FortiGate ' s default operational logic is to try the first entry for contract validation and use the next in the list if the first is unavailable or has high latency or packet loss.

There is no direct correlation between the Weight and the number of FortiGuard-requests. The servers with higher or lower weights may still handle different request volumes based on availability and performance.

The TZ (time zone) value ' s sign (positive or negative) does not affect server preference; it is informational, showing the server ' s location relative to UTC, not a rating metric.

DNS query results for FortiGuard servers are not shown here, and the provided servers are not returned in DNS query order.

This command and interpretation are detailed in the FortiOS Administration Guide’s section describing FortiGuard server selection and contract validation processes.

The correct answer is C. 64.26.151.37 .

The study guide explains the FortiGuard flags shown by diagnose debug rating:

D = Default

I = Initial

T = Timing

F = Failed and specifically: “F = The server is down”

So even though 121.111.236.179 has the lowest RTT in the exhibit, it has the F flag, meaning FortiGate considers that server failed/down , so it will not be chosen.

To determine which active server is selected, the FortiOS administration guide states:

“The server list is sorted first by weight. The server with the smallest RTT appears at the top of the list regardless of weight. … Therefore the top position in the list is selected based on RTT while the other positions are based on weight.”

Among the valid, non-failed choices in the exhibit:

64.26.151.37 → RTT 45

209.22.147.36 → RTT 103

96.45.33.65 → RTT 144

208.91.112.194 → RTT 107

The active server with the lowest RTT is 64.26.151.37 , so that is the server FortiGate will choose.

So the verified answer is: C .

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.