This PCNSA practice question tests your understanding of decryption and monitoring. 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.
Exhibit
admin@PA-220> show decryption policy
name from to source destination service action type
Decrypt-SSH trust untrust 10.0.0.0/24 0.0.0.0/0 any decrypt ssh-proxy
admin@PA-220> show session all
Total sessions: 1
ID Application State Type Src IP:Port Dst IP:Port Protocol Ingress Egress
1 ssh ACTIVE FLOW 10.0.0.10:22 192.168.1.50:22 tcp eth1/1 eth1/2
admin@PA-220> show system log | match ssh
2024-06-15 12:00:00 ssh_decrypt error Failed to decrypt SSH session: unsupported key exchange algorithm. Src: 10.0.0.10 Dst: 192.168.1.50
Refer to the exhibit. An administrator configured SSH decryption, but the firewall logs an error. 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.
Exhibit
admin@PA-220> show decryption policy
name from to source destination service action type
Decrypt-SSH trust untrust 10.0.0.0/24 0.0.0.0/0 any decrypt ssh-proxy
admin@PA-220> show session all
Total sessions: 1
ID Application State Type Src IP:Port Dst IP:Port Protocol Ingress Egress
1 ssh ACTIVE FLOW 10.0.0.10:22 192.168.1.50:22 tcp eth1/1 eth1/2
admin@PA-220> show system log | match ssh
2024-06-15 12:00:00 ssh_decrypt error Failed to decrypt SSH session: unsupported key exchange algorithm. Src: 10.0.0.10 Dst: 192.168.1.50
A
The firewall does not have a certificate installed for SSH decryption.
Why wrong: SSH decryption does not use certificates; it uses key exchange.
B
The SSH session is using a cipher that is not supported by the firewall's decryption engine.
Why wrong: The error specifically mentions key exchange algorithm, not cipher.
C
The SSH key exchange algorithm used by the client or server is not in the firewall's supported list.
The error states 'unsupported key exchange algorithm'. The firewall supports a limited set of algorithms for SSH decryption.
D
The decryption policy is misconfigured because the service is set to 'any' instead of 'ssh'.
Why wrong: The service 'any' is acceptable and would match SSH traffic; the error is not about policy matching.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The SSH key exchange algorithm used by the client or server is not in the firewall's supported list.
The error message indicates 'unsupported key exchange algorithm'. SSH decryption requires the firewall to act as a proxy and re-encrypt the session. If the client or server uses a key exchange algorithm that the firewall does not support, decryption will fail. The exhibit shows a policy for SSH decryption and a session, but the algorithm is not supported.
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 firewall does not have a certificate installed for SSH decryption.
Why it's wrong here
SSH decryption does not use certificates; it uses key exchange.
✗
The SSH session is using a cipher that is not supported by the firewall's decryption engine.
Why it's wrong here
The error specifically mentions key exchange algorithm, not cipher.
✓
The SSH key exchange algorithm used by the client or server is not in the firewall's supported list.
Why this is correct
The error states 'unsupported key exchange algorithm'. The firewall supports a limited set of algorithms for SSH decryption.
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 decryption policy is misconfigured because the service is set to 'any' instead of 'ssh'.
Why it's wrong here
The service 'any' is acceptable and would match SSH traffic; the error is not about policy matching.
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 PCNSA 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 PCNSA 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.
Decryption and Monitoring — This question tests Decryption and Monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The SSH key exchange algorithm used by the client or server is not in the firewall's supported list. — The error message indicates 'unsupported key exchange algorithm'. SSH decryption requires the firewall to act as a proxy and re-encrypt the session. If the client or server uses a key exchange algorithm that the firewall does not support, decryption will fail. The exhibit shows a policy for SSH decryption and a session, but the algorithm is not supported.
What should I do if I get this PCNSA question wrong?
Identify which PCNSA 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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