- A
Set the 'add-route' option to 'enable' on the spoke Phase 1 settings
Why wrong: The 'add-route' option automatically adds routes on the spoke for the remote subnet, but does not create direct spoke-to-spoke tunnels.
- B
Configure dynamic routing (BGP) on all sites and enable route exchange
Dynamic routing (BGP/OSPF) can advertise spoke subnets to each other, allowing direct tunnels to be established if using ADVPN or additional Phase 2 selectors.
- C
Add static routes on the hub pointing to each spoke's subnet via the respective tunnels
Why wrong: Static routes on the hub would route traffic through the hub, not directly between spokes.
- D
Create a separate IPsec VPN between each spoke pair
Why wrong: That would work but is not a change within the hub-and-spoke topology; it's creating a full mesh.
NSE4 Authentication and VPN Practice Question
This NSE4 practice question tests your understanding of authentication and vpn. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
In a hub-and-spoke IPsec VPN topology with FortiGate, the spoke sites cannot communicate directly with each other. What configuration change allows direct spoke-to-spoke communication?
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
Configure dynamic routing (BGP) on all sites and enable route exchange
By default, hub-and-spoke only allows communication between spokes via the hub. To enable direct spoke-to-spoke, you need to add Phase 2 selectors with each other's subnets on the hub or configure dynamic routing (BGP/OSPF) to advertise routes between spokes. Another method is to use ADVPN (Auto Discovery VPN).
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set the 'add-route' option to 'enable' on the spoke Phase 1 settings
Why it's wrong here
The 'add-route' option automatically adds routes on the spoke for the remote subnet, but does not create direct spoke-to-spoke tunnels.
- ✓
Configure dynamic routing (BGP) on all sites and enable route exchange
- ✗
Add static routes on the hub pointing to each spoke's subnet via the respective tunnels
Why it's wrong here
Static routes on the hub would route traffic through the hub, not directly between spokes.
- ✗
Create a separate IPsec VPN between each spoke pair
Why it's wrong here
That would work but is not a change within the hub-and-spoke topology; it's creating a full mesh.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related NSE4 OSPF questions on adjacency and route 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 — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Configure dynamic routing (BGP) on all sites and enable route exchange — By default, hub-and-spoke only allows communication between spokes via the hub. To enable direct spoke-to-spoke, you need to add Phase 2 selectors with each other's subnets on the hub or configure dynamic routing (BGP/OSPF) to advertise routes between spokes. Another method is to use ADVPN (Auto Discovery VPN).
What should I do if I get this NSE4 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related NSE4 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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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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