The correct answer is to check that the Phase 2 proposal settings—specifically encryption, authentication, and Perfect Forward Secrecy (PFS)—match on both peers. This is because the "no matching phase2 proposal" error in the IPsec VPN Phase 2 negotiation occurs when the FortiGate receives a proposal from the remote peer that does not align with its own configured Phase 2 selectors; since Phase 1 successfully established the IKE SA, the mismatch is isolated to the data-plane parameters like AES, SHA, and DH group. On the Fortinet NSE 7 Advanced Security NSE7 exam, this scenario tests your ability to troubleshoot IPsec VPNs by reading `diagnose vpn ike log` output, and a common trap is to mistakenly check Phase 1 settings or firewall policies when the log clearly points to Phase 2. Remember the memory tip: "Phase 1 is the handshake, Phase 2 is the data path—if the log says 'no matching proposal', compare your selectors byte by byte."
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.
A user reports that they cannot connect to a remote office via IPsec VPN. Phase 1 is up, but Phase 2 fails to establish. The administrator runs 'diagnose vpn ike log' and sees 'no matching phase2 proposal'. What should be checked?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Phase 2 proposal settings (encryption, authentication, PFS) match on both peers
The error 'no matching phase2 proposal' indicates that the Phase 2 parameters (encryption, authentication, etc.) do not match between the two endpoints. The administrator should verify the Phase 2 selectors on both sides.
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.
✗
The firewall policies allow IKE traffic
Why it's wrong here
Phase 1 is already up, so IKE traffic is allowed.
✗
The local and remote subnet definitions are correct
Why it's wrong here
Incorrect subnets cause traffic not to be encrypted, but the error message specifically mentions proposal mismatch.
✗
The pre-shared key is correct
Why it's wrong here
Pre-shared key is used in Phase 1, not Phase 2.
✓
The Phase 2 proposal settings (encryption, authentication, PFS) match on both peers
Why this is correct
Mismatched Phase 2 proposals prevent the tunnel from establishing.
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: The Phase 2 proposal settings (encryption, authentication, PFS) match on both peers — The error 'no matching phase2 proposal' indicates that the Phase 2 parameters (encryption, authentication, etc.) do not match between the two endpoints. The administrator should verify the Phase 2 selectors on both sides.
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
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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. You are troubleshooting a VPN phase 2 negotiation failure. The logs show 'no proposal chosen'. What is the MOST likely cause?
hard
A.The remote gateway IP is incorrect
B.The pre-shared key mismatch
C.The IKE version mismatch
✓ D.The phase 2 proposal settings differ between the peers
Why D: Option C is correct because 'no proposal chosen' indicates that the encryption/authentication algorithms proposed by the initiator do not match the responder's configured settings. Option A would cause phase 1 failure. Option B would cause phase 1 failure. Option D is not a direct cause.
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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.
Question Discussion
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