The answer is to verify that the Phase 2 selectors match exactly on both sides and to check for a Perfect Forward Secrecy (PFS) mismatch. This is correct because the "no proposal chosen" error in IPsec VPN Phase 2 troubleshooting indicates that the two peers cannot agree on the security parameters for the data channel, even though Phase 1 authentication succeeded. The most common causes are mismatched local and remote subnet selectors—such as one side using 10.0.0.0/24 while the other expects a different range—or a PFS mismatch, where one side requires PFS but the other has it disabled. On the Fortinet NSE 7 Advanced Security exam, this scenario tests your ability to diagnose Phase 2 failures beyond simple encryption mismatches, often hiding the real issue in selector or PFS settings. A common trap is assuming only the encryption algorithm matters, but the exam emphasizes that selectors must be mirror images. Memory tip: "Selectors mirror, PFS agree—no proposal chosen? Check these three."
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 seems to complete, but Phase 2 fails with 'no proposal chosen'. The administrator checks the Phase 2 configuration and sees the following settings: 'Local address: 10.0.0.0/24, Remote address: 192.168.0.0/24, Proposal: aes256-sha1, Enable Perfect Forward Secrecy (PFS): Disabled'. Which TWO changes would most likely resolve the issue? (Choose two.)
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
✓
Enable PFS on FortiGate
Phase 2 failure with 'no proposal chosen' indicates a mismatch in proposal or selectors. Common causes: PFS mismatch (if remote requires PFS) or selector mismatch (subnets).
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.
✓
Enable PFS on FortiGate
Why this is correct
If the remote side requires PFS, FortiGate must enable it to match.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Changing selector without knowing remote requirements could cause more issues.
✗
Add aes256-sha256 to the Phase 2 proposal
Why it's wrong here
Without knowing remote proposal, adding another may not help if PFS mismatch exists.
✗
Increase the Phase 2 lifetime
Why it's wrong here
Lifetime mismatch usually causes rekey issues, not proposal failure.
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: Enable PFS on FortiGate — Phase 2 failure with 'no proposal chosen' indicates a mismatch in proposal or selectors. Common causes: PFS mismatch (if remote requires PFS) or selector mismatch (subnets).
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.
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?
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 establishes phase 1 but fails phase 2. Which TWO commands are MOST useful to diagnose the phase 2 failure? (Choose two.)
medium
A.diagnose sys session list
B.show vpn ipsec phase2-interface
C.get system performance status
✓ D.diagnose vpn ike config
✓ E.diagnose debug application ike 255
Why D: Options A and D are correct. 'diagnose vpn ike config' shows the IKE configuration including phase 2 proposals and selectors. 'diagnose debug application ike 255' enables detailed IKE debug, which will show the negotiation details including phase 2 failure reasons.
Variation 2. An administrator is troubleshooting an IPsec VPN tunnel that establishes phase 1 but fails to establish phase 2. The phase 2 configuration shows 'set proposal aes128-sha256' on both sides. Which TWO configuration items should the administrator verify?
medium
✓ A.PFS (Perfect Forward Secrecy) settings
B.The local authentication method (certificate vs pre-shared key)
C.The encryption algorithm for phase 2
✓ D.The local and remote subnets defined in phase 2 (proxy IDs)
E.The pre-shared key
Why A: Even if phase 1 succeeds, phase 2 can fail due to mismatched proxy IDs (local/remote subnets) or mismatched PFS settings. Authentication method and encryption algorithm are phase 1 parameters.
Variation 3. An administrator is troubleshooting an IPsec VPN where phase 1 is up but phase 2 fails. Which two debug commands would be MOST helpful in diagnosing the phase 2 issue? (Choose TWO.)
medium
A.diagnose sys session list
B.diagnose debug application ipsec -1
✓ C.diagnose vpn ipsec phase2-config
D.get vpn ipsec tunnel details
✓ E.diagnose debug application ike -1
Why C: Phase 2 uses IPsec SA negotiation, which is logged by IKE debug. Additionally, checking the phase 2 configuration can reveal mismatches. The correct commands are A and D.
Last reviewed: Jun 21, 2026
Question Discussion
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