The answer is a Phase 1 encryption or hash algorithm mismatch. The "no acceptable proposal" error occurs because the initiator sends an IKE proposal that does not match any proposal configured on the responder, which is a classic Phase 1 mismatch. In IPsec negotiation, Phase 1 establishes the secure channel by agreeing on parameters like encryption (e.g., AES) and hashing (e.g., SHA-1); if the two sides don't share a common set, the responder rejects the proposal with this exact debug output. On the Fortinet NSE 4 Network Security Professional NSE4 exam, this error tests your understanding of IKE Phase 1 configuration, often appearing as a trap where candidates mistakenly blame Phase 2 settings or firewall policies. A common memory tip is to think of "no acceptable proposal" as a "first date rejection"—the initiator's offer doesn't match the responder's preferences, so the handshake fails before any Phase 2 negotiation begins.
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.
You run 'diagnose debug application ike -1' and see the following output: 'Initiator: no acceptable proposal'. What is the MOST likely cause of this error?
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
✓
The Phase 1 encryption or hash algorithm is mismatched
The 'no acceptable proposal' error indicates that the IKE proposal sent by the initiator does not match any proposal configured on the responder. This is a Phase 1 mismatch.
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.
✗
The pre-shared key is incorrect
Why it's wrong here
Incorrect PSK would give a different error, such as authentication failure.
✓
The Phase 1 encryption or hash algorithm is mismatched
Why this is correct
Mismatched proposals cause this exact error.
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.
✗
The remote gateway is not reachable
Why it's wrong here
Unreachable remote gateway would result in timeout, not this message.
✗
The firewall policy is blocking UDP port 500
Why it's wrong here
Blocking port 500 would prevent IKE packets from reaching the FortiGate.
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: The Phase 1 encryption or hash algorithm is mismatched — The 'no acceptable proposal' error indicates that the IKE proposal sent by the initiator does not match any proposal configured on the responder. This is a Phase 1 mismatch.
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.
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Question Discussion
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