- A
Change the IPsec mode from policy-based to route-based
Why wrong: While route-based can simplify routing, the key issue is Phase 2 selectors and policies, not the mode itself.
- B
Modify the Phase 2 selectors on the hub to include both spoke subnets and add firewall policies allowing traffic between the spoke networks
The hub's Phase 2 selectors must match the traffic it needs to forward between spokes. Additionally, firewall policies must permit the traffic.
- C
Enable 'add-route' on the hub's Phase 1 settings
Why wrong: 'add-route' automatically adds routes to the hub's routing table, but does not create policies or adjust Phase 2 selectors for inter-spoke traffic.
- D
Configure a static route on each spoke pointing to the other spoke's subnet via the tunnel
Why wrong: Spokes are not directly connected; they must go through the hub. Routes on the hub are more critical.
Quick Answer
The answer is to modify the Phase 2 selectors on the hub to include both spoke subnets and add firewall policies allowing traffic between the spoke networks. This is required because, in a hub-and-spoke VPN, the hub’s Phase 2 selectors define which traffic is permitted to traverse each IPsec tunnel; by default, each spoke’s selector only matches its own local subnet with the hub, so spoke-to-spoke traffic is dropped at the hub’s encryption engine. Adding both spoke subnets (or using 0.0.0.0/0) to the hub’s Phase 2 selectors ensures the hub can decrypt and re-encrypt the traffic, while separate firewall policies explicitly permit forwarding between the spoke networks. On the Fortinet NSE 4 exam, this tests your understanding of IPsec tunnel negotiation and policy routing—a common trap is assuming that simply adding firewall policies is enough, forgetting that Phase 2 selectors act as a traffic filter. Memory tip: “Phase 2 picks the path, policy permits the pass”—both must align for spoke-to-spoke traffic to flow through the hub.
NSE4 Authentication and VPN Practice Question
This NSE4 practice question tests your understanding of authentication and vpn. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Modify the Phase 2 selectors on the hub to include both spoke subnets and add firewall policies allowing traffic between the spoke networks
Option C is correct. For spoke-to-spoke traffic to pass through the hub, the hub must have firewall policies allowing traffic between the spoke networks, and the Phase 2 selectors on the hub must include both spoke subnets (or use 0.0.0.0/0 to allow all traffic).
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Change the IPsec mode from policy-based to route-based
Why it's wrong here
While route-based can simplify routing, the key issue is Phase 2 selectors and policies, not the mode itself.
- ✓
Modify the Phase 2 selectors on the hub to include both spoke subnets and add firewall policies allowing traffic between the spoke networks
- ✗
Enable 'add-route' on the hub's Phase 1 settings
Why it's wrong here
'add-route' automatically adds routes to the hub's routing table, but does not create policies or adjust Phase 2 selectors for inter-spoke traffic.
- ✗
Configure a static route on each spoke pointing to the other spoke's subnet via the tunnel
Why it's wrong here
Spokes are not directly connected; they must go through the hub. Routes on the hub are more critical.
Common exam traps
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
- CIDR notation defines the prefix length.
- Block size helps identify subnet boundaries.
- Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
- The required host count determines the smallest suitable subnet.
TExam Day Tips
- Write the block size before choosing the subnet.
- Check whether the question asks for hosts, subnets or a specific address range.
- Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A network engineer segments a warehouse floor into three subnets: 20 scanners, 5 printers, and 2 management hosts. Picking the wrong mask wastes addresses or leaves too few usable hosts. Exam questions test whether you can apply CIDR notation, calculate block size, and identify the correct usable-host range for a given prefix.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related NSE4 subnetting questions on CIDR, address ranges, and subnet selection.
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Authentication and VPN — study guide chapter
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FAQ
Questions learners often ask
What does this NSE4 question test?
Authentication and VPN — This question tests Authentication and VPN — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Modify the Phase 2 selectors on the hub to include both spoke subnets and add firewall policies allowing traffic between the spoke networks — Option C is correct. For spoke-to-spoke traffic to pass through the hub, the hub must have firewall policies allowing traffic between the spoke networks, and the Phase 2 selectors on the hub must include both spoke subnets (or use 0.0.0.0/0 to allow all traffic).
What should I do if I get this NSE4 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related NSE4 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
About these practice questions
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Last reviewed: Jun 21, 2026
This NSE4 practice question is part of Courseiva's free Fortinet certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the NSE4 exam.
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