The answer is that the IPsec phase 2 proposal does not include the OSPF multicast IP address 224.0.0.5. This is the most likely cause because OSPF relies on multicast hello packets sent to 224.0.0.5 to discover and maintain neighbor adjacencies; if the IPsec VPN tunnel’s phase 2 selector does not explicitly permit this multicast traffic, the packets are dropped, leaving the neighbor stuck in the INIT state. On the Fortinet NSE 7 Advanced Security NSE7 exam, this scenario tests your understanding of how IPsec security policies interact with dynamic routing protocols—a common trap is to focus on OSPF timers or authentication instead of the underlying VPN configuration. Remember that OSPF over IPsec requires both unicast and multicast traffic to pass, so always verify that the phase 2 proposal includes 224.0.0.5. A helpful memory tip: “OSPF needs a multicast pass, or INIT will be your class.”
NSE7 Advanced VPN and Zero Trust Practice Question
This NSE7 practice question tests your understanding of advanced vpn and zero trust. 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.
A FortiGate is configured with OSPF over an IPsec VPN tunnel to exchange routes with a remote site. The OSPF neighbor states are stuck in 'INIT' and never progress to 'FULL'. What is the MOST likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Clue: "never"
Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
Why wrong: MTU issues typically cause problems in EXSTART/EXCHANGE states, not INIT.
B
OSPF authentication is not configured on both sides
Why wrong: Missing authentication would cause the neighbor to go down to DOWN, not stuck in INIT.
C
The IPsec phase 2 proposal does not include the OSPF multicast IP address (224.0.0.5)
OSPF uses multicast address 224.0.0.5. The IPsec SA must be configured to allow this traffic; if the proxy ID does not include the multicast address, OSPF packets are dropped.
D
The OSPF hello interval is too short
Why wrong: Hello interval mismatch would cause the neighbor to be stuck in EXSTART, not INIT.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The IPsec phase 2 proposal does not include the OSPF multicast IP address (224.0.0.5)
OSPF requires multicast support (224.0.0.5) to form adjacencies. Without multicast over the VPN tunnel, OSPF cannot exchange hello packets properly.
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.
✗
The MTU on the VPN interface is too high
Why it's wrong here
MTU issues typically cause problems in EXSTART/EXCHANGE states, not INIT.
✗
OSPF authentication is not configured on both sides
Why it's wrong here
Missing authentication would cause the neighbor to go down to DOWN, not stuck in INIT.
✓
The IPsec phase 2 proposal does not include the OSPF multicast IP address (224.0.0.5)
Why this is correct
OSPF uses multicast address 224.0.0.5. The IPsec SA must be configured to allow this traffic; if the proxy ID does not include the multicast address, OSPF packets are dropped.
Clue confirmation
The clue words "most likely", "never" in the question point toward this answer.
Hello interval mismatch would cause the neighbor to be stuck in EXSTART, not INIT.
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 NSE7 OSPF questions on adjacency and route selection.
Advanced VPN and Zero Trust — This question tests Advanced VPN and Zero Trust — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The IPsec phase 2 proposal does not include the OSPF multicast IP address (224.0.0.5) — OSPF requires multicast support (224.0.0.5) to form adjacencies. Without multicast over the VPN tunnel, OSPF cannot exchange hello packets properly.
What should I do if I get this NSE7 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 NSE7 OSPF questions on adjacency and route selection.
Are there clue words in this question I should notice?
Yes — watch for: "most likely", "never". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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