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Authentication and VPN

Practise Fortinet NSE 4 Network Security Professional NSE4 Authentication and VPN practice questions — original exam-style scenarios with answer choices, explanations, and analysis of common mistakes.

73 questions15 easy37 medium21 hard

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What to know about Authentication and VPN

Authentication and VPN questions test whether you can apply the concept in context, not just recognise a definition.

How the topic appears in realistic exam-style scenarios.

Which detail in the question changes the correct answer.

How to eliminate plausible but wrong options.

How to connect the question back to the wider exam objective.

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Common Authentication and VPN exam traps

  • Answering from memory before reading the full scenario.
  • Missing a constraint such as cost, availability, security, scope or command context.
  • Choosing a broad answer when the question asks for the most specific fix.
  • Ignoring why the wrong options are tempting.

Question index

All Authentication and VPN questions (73)

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1

A FortiGate with multiple VDOMs is configured for FSSO with Active Directory polling. Users in VDOM1 are authenticated correctly, but users in VDOM2 are not. What should be checked FIRST?

Medium
2

A FortiGate is configured in an HA active-passive cluster. When the active unit fails, the passive unit takes over, but IPsec VPN tunnels fail to re-establish. The configuration is synchronized. What is the most likely cause?

Hard
3

An admin needs to authenticate remote users connecting via SSL VPN. The users are in an Active Directory domain. Which authentication method should be configured on the FortiGate to allow users to log in with their domain credentials?

Easy
4

Which authentication method allows FortiGate to authenticate users against an Active Directory domain without storing domain credentials locally?

Easy
5

A FortiGate is configured with FSSO using a DC agent. Users authenticate to the domain, but the firewall policy using FSSO groups is not matching traffic. The admin runs 'diagnose debug authd fsso list' and sees user entries. However, the traffic is being denied by the default deny policy. What is the most likely issue?

Hard
6

An administrator needs to configure a hub-and-spoke IPsec VPN topology. Which TWO settings must be configured on the hub FortiGate to allow spokes to communicate with each other through the hub?

Medium
7

A company wants to use captive portal authentication on a guest Wi-Fi network. The FortiGate is connected to the switchport of the access point. Which firewall configuration is required to redirect unauthenticated users to the captive portal?

Medium
8

An administrator is troubleshooting an IPsec VPN between two FortiGates. Phase 1 is up but Phase 2 is down. The admin runs 'diagnose vpn ike log' and sees 'no matching proposal'. To resolve this issue, which TWO settings should be checked on both ends?

Medium
9

An administrator configures a captive portal on the FortiGate to authenticate guest users via a local user database. Users can connect to the SSID, but after entering credentials on the captive portal, they are not redirected to the internet. What is the most likely missing configuration?

Medium
10

A network administrator configures an IPsec VPN between two FortiGate devices. Phase 1 completes successfully, but Phase 2 fails to establish. The administrator runs 'diagnose vpn ike log' and sees the error 'proposal mismatch'. What is the MOST likely cause?

Medium
11

A FortiGate administrator is configuring ZTNA to secure access to an internal application. The administrator creates a ZTNA access proxy and a ZTNA rule. However, users connecting from the internet receive a 403 Forbidden error. The administrator verifies that the users are authenticated and the application is reachable. What is the MOST likely cause?

Hard
12

A FortiGate administrator has configured a hub-and-spoke IPsec VPN. The hub FortiGate has two Phase 2 selectors with spokes, but traffic between spokes is not routed via the hub. What must be configured on the hub to allow spoke-to-spoke communication?

Hard
13

An administrator is configuring a site-to-site IPsec VPN between two FortiGates. After applying the configuration, the VPN status shows 'down'. Phase 1 parameters are identical on both sides. What is the most likely cause of the failure?

Medium
14

A FortiGate administrator notices that the IPsec VPN tunnel is established but traffic is not passing. The firewall policy allowing traffic from the remote subnet to the local subnet is in place. What is the MOST likely cause?

Hard
15

An administrator runs 'diagnose debug application ike -1' and sees the following output: ike 0:come to x.x.x.x:500, IKEv1, cookie 123456789abcdef0 ike 0:incoming IKE packet: src y.y.y.y:500, dst x.x.x.x:500, len 456 ike 0:send IKE packet: src x.x.x.x:500, dst y.y.y.y:500, len 456 ike 0:phase 1 negotiation failed due to time out. What is the likely cause?

Hard
16

An administrator is troubleshooting an IPsec VPN tunnel that is not establishing. The Phase 1 status shows 'down'. Which TWO commands can help diagnose the issue? (Choose TWO.)

Medium
17

A FortiGate administrator is troubleshooting an IPsec VPN that fails to establish. The Phase 1 status shows 'init' and then resets. The administrator runs 'diagnose debug application ike -1' and sees the message 'no acceptable proposal'. Which TWO parameters are MOST likely mismatched?

Hard
18

You run 'diagnose sys session filter dport 443' and see the following output: proto=6 proto_state=01 duration=3600 expire=3599 What does this indicate?

Hard
19

An administrator configures a dial-up IPsec VPN using IKEv2 with certificates. Remote users can connect, but traffic is not routed through the tunnel. The Phase 1 status shows 'up', but Phase 2 shows 'down'. What is the most likely issue?

Hard
20

A FortiGate admin wants to implement ZTNA to secure access to an internal application. Which TWO components are required for a basic ZTNA configuration?

Medium
21

A FortiGate administrator is setting up a dial-up IPsec VPN for remote employees. Each employee uses a FortiClient. Which authentication method should be used to allow individual user identities?

Medium
22

Refer to the exhibit. A network administrator configured an IPsec VPN between the main office and a branch office. Remote users at the branch office report that they cannot access resources in the main office. The tunnel status shows up on both sides. What is the most likely cause of the connectivity issue?

Easy
23

An administrator is configuring a dial-up IPsec VPN for remote users. Which TWO settings are required on the FortiGate for the dial-up server? (Choose two.)

Medium
24

Which mode of SSL VPN provides full network-layer access to the remote network, allowing any application to function as if the client is directly connected?

Easy
25

You are configuring a route-based IPsec VPN with BGP over the tunnel. After Phase 2 is up, the BGP session does not establish. You run 'diagnose debug ipsec' and see no errors. What should you check next?

Medium
26

An administrator runs 'diagnose debug application fnbamd -1' on a FortiGate to troubleshoot authentication issues. The output shows that the FortiGate successfully contacts the LDAP server but the user authentication fails. What does this indicate?

Medium
27

What is the primary difference between route-based and policy-based IPsec VPNs on a FortiGate?

Easy
28

A FortiGate admin is configuring a hub-and-spoke IPsec VPN. The hub has multiple phase 2 configurations for each spoke. The spokes can communicate with the hub but not with each other. The admin wants to allow spoke-to-spoke traffic through the hub. Which configuration change is required on the hub?

Medium
29

An administrator needs to authenticate users on a FortiGate using RADIUS. Which TWO of the following are required to configure RADIUS authentication?

Easy
30

A FortiGate administrator is configuring a route-based IPsec VPN between two FortiGate devices. After setting up the tunnel and firewall policies, traffic does not flow. The administrator runs 'diagnose vpn tunnel list' and sees the tunnel is up. 'get router info routing-table all' shows routes on both sides. However, pings from the local network to the remote network fail. What is the MOST likely cause?

Hard
31

A client connects to a FortiGate SSL VPN in web mode. The user can access internal web applications but cannot ping or RDP to servers. The administrator wants to allow these services. What must be changed?

Medium
32

An administrator has configured an SSL VPN with tunnel mode and split tunneling enabled. However, remote users report that all internet traffic is going through the VPN tunnel. What is the MOST likely cause?

Hard
33

A company uses Fortinet Single Sign-On (FSSO) to authenticate users for firewall policies. The FSSO collector agent is installed on a Windows server and configured with Active Directory polling. What does the collector agent do?

Easy
34

An administrator wants to implement ZTNA (Zero Trust Network Access) on a FortiGate to secure access to an internal application. Which TWO components are essential for a ZTNA configuration?

Medium
35

Which of the following best describes the purpose of a captive portal on a FortiGate?

Easy
36

A company requires two-factor authentication for SSL VPN access. They already have an LDAP server for user credentials. Which TWO components are necessary to implement this?

Medium
37

A network administrator is troubleshooting an IPsec VPN tunnel between two FortiGates. Phase 1 is up, but Phase 2 fails to establish. The debug command 'diagnose vpn ike log' shows: 'no suitable proposal found'. What is the most likely cause?

Medium
38

A network admin configures an IPsec VPN between two FortiGates using IKEv2. Phase 1 completes successfully, but Phase 2 fails to establish. The admin runs 'diagnose vpn ike log' and sees the error 'proposal mismatch'. What is the most likely cause?

Medium
39

What is the primary advantage of using IKEv2 over IKEv1 for IPsec VPN?

Medium
40

A network administrator configures an IPsec VPN between two FortiGates using IKEv1 main mode. The Phase 1 negotiation fails with the error 'no proposal chosen'. The administrator checks both sides and confirms the IKE version, encryption algorithm (AES256), authentication (SHA256), and Diffie-Hellman group (14) match. Which additional parameter is MOST likely mismatched?

Medium
41

An administrator configures a route-based IPsec VPN between two FortiGates. The Phase 1 and Phase 2 are up. The administrator adds a static route on each FortiGate pointing to the remote subnet via the virtual tunnel interface (e.g., 'to_remote'). Traffic between the subnets fails. What is the MOST likely missing configuration?

Medium
42

A network administrator is troubleshooting an IPsec VPN tunnel between two FortiGates. The tunnel is established, but traffic is not passing. The administrator runs 'diagnose vpn tunnel list' and sees the tunnel is up. Which two additional diagnostics should the administrator run to isolate the issue?

Medium
43

Which IPsec VPN mode is typically used when the VPN peer has a dynamic public IP address?

Easy
44

A network administrator has configured an IPsec VPN between two FortiGate devices. The Phase 1 proposal includes AES256-SHA256-DH14. The Phase 2 proposal includes AES128-SHA1. The VPN tunnel fails to establish. Which of the following is the MOST likely cause?

Medium
45

A FortiGate admin is configuring a dial-up IPsec VPN for remote users. The users have dynamic IP addresses. Which Phase 1 configuration is appropriate?

Medium
46

A FortiGate is configured with FSSO for firewall authentication. Users report they are prompted for credentials every time they access the internet, even though they are logged into the domain. What is the most likely cause?

Medium
47

An administrator wants to use Active Directory credentials to authenticate firewall administrators. Which authentication server type should be configured on the FortiGate?

Easy
48

You run the command 'diagnose vpn ike log filter name vpn1' and then 'diagnose vpn ike log filter type phase1'. The log shows: 'IKEv1 exchange:f4470f07:00000000: responder: main mode: received IKE_SA_INIT (aggressive mode not allowed)'. What is the problem?

Hard
49

A FortiGate administrator runs 'diagnose vpn tunnel list' and sees the following output for an IPsec tunnel: 'status: up', 'incoming: 0 packets', 'outgoing: 100 packets'. Phase 1 and Phase 2 both show state 'up'. What is the MOST likely cause of zero incoming packets?

Hard
50

You run the CLI command 'diagnose vpn ike gateway list' and see that an IPsec VPN gateway is in 'up' state with 'initiator' mode, but no Phase 2 selectors are established. What is the most likely cause?

Hard
51

A FortiGate administrator wants to authenticate VPN users against an existing LDAP server. The administrator creates an LDAP user group on the FortiGate. What additional configuration is REQUIRED to use this group for IPsec VPN authentication?

Easy
52

A network administrator wants to implement two-factor authentication for SSL VPN users using FortiToken. The users are already authenticated against an LDAP server. Which configuration step is required to enforce two-factor authentication?

Medium
53

An administrator configures FSSO (Fortinet Single Sign-On) with Active Directory polling. Users report that their web traffic is being blocked by the firewall even though they are logged into the domain. Which CLI command can the administrator use to verify the FSSO login status for a specific user?

Hard
54

An administrator wants to restrict SSL VPN access to only users who have a valid client certificate issued by the company's internal CA. Which setting should be configured?

Easy
55

Which of the following FortiGate features allows users to authenticate using a one-time password generated by a mobile app?

Easy
56

A network admin configures a site-to-site IPsec VPN between two FortiGates using IKEv1 main mode. The tunnel establishes successfully, but no traffic passes. What is the MOST likely cause?

Medium
57

An administrator runs 'diagnose vpn ike gateway list' on a FortiGate and sees the following output for a dial-up IPsec VPN: gateway name: 'dialup' version: IKEv1 mode: aggressive local IP: 203.0.113.1 remote IP: 0.0.0.0 state: up peers: 0 What does 'peers: 0' indicate?

Hard
58

A FortiGate administrator is configuring an SSL VPN web mode portal. The administrator wants users to access only a specific internal web application (https://internal-app.company.local) and nothing else. Which SSL VPN setting should be configured to achieve this?

Medium
59

A remote user connects via SSL VPN web mode but cannot access internal resources. The SSL VPN portal is configured with the default settings. What is the most likely reason?

Medium
60

An administrator configures a dial-up IPsec VPN with IKEv2 to allow remote users to connect. The Phase 1 is set to use certificate-based authentication (PKI). Users can establish Phase 1, but Phase 2 fails with 'no proposal chosen'. The administrator checks the Phase 2 proposal: AES256-SHA256, and the remote network is 10.0.0.0/8 (the corporate LAN). What is the MOST likely cause?

Hard
61

A FortiGate administrator is configuring a hub-and-spoke IPsec VPN. The hub has multiple Phase 2 selectors for each spoke. What is the recommended way to simplify configuration on the hub when adding new spokes?

Medium
62

A FortiGate admin is troubleshooting an IPsec VPN that fails to establish. The output of 'diagnose debug application ike -1' shows: 'IKE: No proposal chosen from x.x.x.x'. The admin checks the Phase1 configuration. Which of the following mismatches could cause this error? (Choose three.)

Hard
63

You are troubleshooting an SSL VPN connection. The user can reach the SSL VPN portal but cannot ping or access any internal resources. The portal shows the user as authenticated. Which configuration is MOST likely missing?

Hard
64

An administrator wants to authenticate VPN users against an external LDAP server. Which authentication method should be configured in the user group for the SSL VPN portal?

Easy
65

A FortiGate administrator wants to configure a dial-up IPsec VPN where remote users connect using VPN clients with pre-shared key authentication. The company has recently experienced a data breach where the PSK was compromised. What is the best method to improve security without changing all clients immediately?

Medium
66

A FortiGate administrator has configured a route-based IPsec VPN. After Phase 2 is up, traffic is not passing. The administrator verifies that the firewall policy allows traffic and the routes are correct. What should the administrator check next?

Medium
67

A FortiGate administrator configures a captive portal on a VDOM to authenticate users connecting to a guest SSID. The authentication method is set to LDAP. Users can reach the captive portal login page, but after entering valid credentials, they receive an authentication failure. The LDAP server is reachable from the FortiGate. What is the MOST likely cause?

Medium
68

A company has multiple branch offices connected via IPsec VPN in a hub-and-spoke topology. They want to enable direct communication between branch offices without routing traffic through the hub. Which THREE configurations are required on the hub FortiGate? (Choose three.)

Hard
69

A FortiGate administrator is troubleshooting a dial-up IPsec VPN where remote users can connect but traffic does not pass. The Phase 1 and Phase 2 status show 'up'. The administrator runs 'diagnose vpn tunnel list' and sees the tunnel is up. However, 'diagnose sys session list' shows no sessions for the remote user's IP. What is the MOST likely cause?

Hard
70

A FortiGate administrator is configuring IPsec VPN between two sites. The Phase 1 negotiation fails with the error 'no proposal chosen'. Which two settings must match on both VPN peers?

Medium
71

A FortiGate administrator is troubleshooting an SSL VPN connection issue. Users can connect but cannot access internal resources. The administrator checks the SSL VPN policy and confirms it allows access to the internal subnet. What should the administrator check next?

Medium
72

An administrator has configured an SSL VPN. Remote users can connect and authenticate but cannot access internal resources. The SSL VPN policy allows all traffic from the SSL VPN interface to internal servers. What is the MOST likely missing configuration?

Medium
73

What is the primary advantage of using route-based IPsec VPN over policy-based IPsec VPN?

Easy

Frequently asked questions

What does the Authentication and VPN domain cover on the NSE4 exam?
Authentication and VPN questions test whether you can apply the concept in context, not just recognise a definition.
How many questions are in this domain?
This page lists all 73 Authentication and VPN questions in the NSE4 question bank. The actual exam draws from this domain proportionally to its weighting in the official exam blueprint.
What is the best way to practise this domain?
Start with a short focused session (10 questions) to identify gaps, then work through explanations. Repeat with a longer session once the weak areas feel solid.
Can I practise only Authentication and VPN questions?
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