The answer is that the firewall is not configured with the root CA certificate. When a Palo Alto Networks firewall performs inbound decryption for public-facing web servers, it re-encrypts the traffic using the imported server certificate, but it must also present the full certificate chain to clients. Without the root CA certificate installed on the firewall, the chain is incomplete, causing clients to see an untrusted certificate warning because the issuing certificate authority is not recognized. On the PCNSA exam, this scenario tests your understanding of inbound inspection decryption and certificate chain validation—a common trap is assuming that importing only the server certificate and private key is sufficient. Remember, the firewall acts as a proxy; it needs the root CA to prove the certificate’s legitimacy. Memory tip: think “root before route”—the root CA must be present before traffic can be securely decrypted and re-encrypted without warnings.
PCNSA Decryption and Monitoring Practice Question
This PCNSA practice question tests your understanding of decryption and monitoring. 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 organization uses inbound inspection decryption for their public-facing web servers. They have imported the server's certificate and private key into the firewall. However, some clients report 'untrusted certificate' warnings. What is the most likely cause?
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.
The server's certificate is using an unsupported cipher
Why wrong: Unsupported ciphers cause handshake failure, not an untrusted certificate warning.
B
The decryption profile's 'Unsupported Modes' is set to 'Block'
Why wrong: Blocking unsupported modes would cause a connection failure, not an untrusted warning.
C
The decryption policy is not matching the traffic
Why wrong: If the policy didn't match, traffic would not be decrypted and the server would present its own certificate, so no untrusted warning from firewall.
D
The firewall is not configured with the root CA certificate
Without the full chain, the firewall sends only the server certificate, which browsers may not trust.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The firewall is not configured with the root CA certificate
When a firewall performs inbound inspection decryption, it re-encrypts traffic using the server's certificate. If the firewall does not have the root CA certificate that issued the server's certificate, the firewall cannot present a complete certificate chain to clients. Clients then see the certificate as untrusted because the issuing CA is not recognized, even though the server's certificate and private key are correctly imported.
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 server's certificate is using an unsupported cipher
Why it's wrong here
Unsupported ciphers cause handshake failure, not an untrusted certificate warning.
✗
The decryption profile's 'Unsupported Modes' is set to 'Block'
Why it's wrong here
Blocking unsupported modes would cause a connection failure, not an untrusted warning.
✗
The decryption policy is not matching the traffic
Why it's wrong here
If the policy didn't match, traffic would not be decrypted and the server would present its own certificate, so no untrusted warning from firewall.
✓
The firewall is not configured with the root CA certificate
Why this is correct
Without the full chain, the firewall sends only the server certificate, which browsers may not trust.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Palo Alto Networks often tests the distinction between importing the server certificate (for re-encryption) and importing the root CA certificate (for chain completeness), leading candidates to assume the server certificate alone is sufficient for trust.
Detailed technical explanation
How to think about this question
In inbound inspection decryption, the firewall acts as a TLS proxy: it decrypts the client-to-server traffic, inspects it, then re-encrypts it using the server's certificate. For the client to trust the re-encrypted connection, the firewall must present the full certificate chain, including the root CA certificate. If the root CA certificate is not imported into the firewall's trust store, the firewall cannot include it in the ServerHello, causing the client to treat the certificate as self-signed or untrusted. This is distinct from forward proxy decryption, where the firewall generates its own certificate signed by an internal CA.
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.
TExam Day Tips
→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 exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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 firewall is not configured with the root CA certificate — When a firewall performs inbound inspection decryption, it re-encrypts traffic using the server's certificate. If the firewall does not have the root CA certificate that issued the server's certificate, the firewall cannot present a complete certificate chain to clients. Clients then see the certificate as untrusted because the issuing CA is not recognized, even though the server's certificate and private key are correctly imported.
What should I do if I get this PCNSA question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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