The answer is the Diffie-Hellman group and the encryption algorithm. When an IPsec VPN Phase 1 proposal mismatch triggers a 'no acceptable proposal' error, it means the two peers cannot agree on a common set of security parameters during the Internet Key Exchange (IKE) negotiation. The Fortinet NSE 7 Advanced Security NSE7 exam frequently tests this by asking which two of the four Phase 1 attributes—encryption, authentication, Diffie-Hellman group, or key lifetime—are most commonly misconfigured, with the Diffie-Hellman group and encryption algorithm being the primary culprits because they are often set to incompatible values across different vendors or firmware versions. A common trap is assuming key lifetimes are the issue, but mismatched lifetimes typically cause rekey failures, not initial proposal rejection. Remember the memory tip: "DH and Encrypt are the first to inspect" when you see 'no acceptable proposal' in your debug output.
NSE7 Troubleshooting and Diagnostics Practice Question
This NSE7 practice question tests your understanding of troubleshooting and diagnostics. 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.
An administrator is troubleshooting an IPsec VPN tunnel that fails to establish Phase 1. The debug output shows 'no acceptable proposal'. Which TWO configuration parameters should be checked to resolve this issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Encryption algorithm
Phase 1 proposal mismatch is typically due to differences in encryption algorithms, authentication methods, Diffie-Hellman groups, or key lifetimes.
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.
✓
Encryption algorithm
Why this is correct
Mismatched encryption algorithms cause proposal failure.
IKE version mismatch typically results in no response, not proposal failure.
✗
Pre-shared key
Why it's wrong here
Pre-shared key mismatch causes authentication failure, not 'no acceptable proposal'.
✗
Local and remote subnets
Why it's wrong here
Subnets are Phase 2 parameters, not Phase 1.
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 NSE7 subnetting questions on CIDR, address ranges, and subnet selection.
Troubleshooting and Diagnostics — This question tests Troubleshooting and Diagnostics — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Encryption algorithm — Phase 1 proposal mismatch is typically due to differences in encryption algorithms, authentication methods, Diffie-Hellman groups, or key lifetimes.
What should I do if I get this NSE7 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 NSE7 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
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. An administrator is troubleshooting an IPsec VPN tunnel that fails to establish. The Phase 1 status shows 'init' and the debug output indicates 'no suitable proposal found'. The remote peer is a third-party VPN device. Which of the following is the MOST likely cause?
hard
A.The pre-shared key is incorrect on one side
B.The remote peer's IP address is not reachable
✓ C.The IKE version or encryption algorithm does not match between the peers
D.The firewall policy allowing the VPN traffic is missing
Why C: Option C is correct. 'No suitable proposal found' means the local and remote devices do not share a common IKE proposal (encryption, authentication, DH group, etc.). This is a proposal mismatch in Phase 1.
Last reviewed: Jun 21, 2026
Question Discussion
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This NSE7 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 NSE7 exam.
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