The answer is a mismatch in the local and remote identifiers. Even when IKE version, encryption (AES256), authentication (SHA256), and Diffie-Hellman group (14) are identical on both FortiGates, IKEv1 main mode requires the peer’s identity—typically the IP address or FQDN—to match what is configured as the remote ID on the opposite side. If the local ID on one FortiGate does not correspond to the remote ID expected by the other, the Phase 1 negotiation fails with the “no proposal chosen” error, because main mode exchanges identities before establishing a secure channel. On the Fortinet NSE 4 exam, this is a classic trap: candidates often verify only the cryptographic parameters and overlook the identity configuration, which is a separate field in the Phase 1 settings. A common memory tip is to think “main mode means main ID match”—if the IDs don’t align, the tunnel won’t form, regardless of perfect crypto alignment.
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.
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?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Local and remote identifiers (local ID / remote ID)
Main mode requires the local and remote identifiers to match or be correctly configured. Often the local ID (such as the IP address or FQDN) is mismatched, causing negotiation failure despite other parameters matching.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Pre-shared key
Why it's wrong here
A pre-shared key mismatch would typically result in a different error, such as 'authentication failed'.
✗
IKE version (IKEv2)
Why it's wrong here
The administrator confirmed IKE version matches (IKEv1).
✗
Phase 2 encryption algorithm
Why it's wrong here
Phase 1 negotiation occurs before Phase 2; the error is during Phase 1.
✓
Local and remote identifiers (local ID / remote ID)
Why this is correct
In main mode, identifiers are exchanged. A mismatch of local or remote ID can cause 'no proposal chosen'.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the NSE4 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which NSE4 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Authentication and VPN — This question tests Authentication and VPN — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Local and remote identifiers (local ID / remote ID) — Main mode requires the local and remote identifiers to match or be correctly configured. Often the local ID (such as the IP address or FQDN) is mismatched, causing negotiation failure despite other parameters matching.
What should I do if I get this NSE4 question wrong?
Identify which NSE4 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". 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?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. 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
A.Pre-shared key and local ID
B.Dead peer detection interval and retry count
C.Remote gateway IP and Phase 2 selectors
✓ D.Encryption algorithm and authentication algorithm
Why D: The proposal (encryption and authentication algorithms) and the Diffie-Hellman group must match between peers for Phase 1 to succeed. These are the key parameters negotiated during Phase 1.
Last reviewed: Jun 21, 2026
Question Discussion
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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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