PCNSA Decryption and Monitoring Practice Question
Exhibit
admin@PA-220> show decryption policy name from to source destination service action type Decrypt-Traffic trust untrust 10.0.0.0/24 0.0.0.0/0 any decrypt ssl-forward-proxy admin@PA-220> show ssl-decrypt certificate-status Certificate: PA-Forward-Proxy-CA Issuer: CN=PA-Forward-Proxy-CA Valid: 2024-01-01 to 2025-01-01 Status: valid admin@PA-220> show system log | match ssl 2024-06-15 10:30:22 ssl_decrypt error Certificate is not trusted by client. Src: 10.0.0.5 Dst: 93.184.216.34
Refer to the exhibit. A user reports that they receive a certificate warning when accessing https://example.com. The firewall is configured to decrypt SSL traffic. What is the most likely cause?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The client device does not have the firewall's CA certificate installed in its trusted root store.
The log shows an error 'Certificate is not trusted by client'. This typically occurs when the firewall's decryption CA certificate is not installed in the client's trusted root store. The firewall's certificate is valid, but the client does not trust it.
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 web server's certificate is invalid and the firewall is not configured to block untrusted certificates.
Why it's wrong here
The firewall decrypts and re-signs traffic, so a user sees the firewall's certificate, not the web server's; an invalid server certificate would not reach the browser. This is tempting because invalid server certificates normally cause warnings, but that applies only when decryption is bypassed or the site is excluded from the policy.
- ✓
The client device does not have the firewall's CA certificate installed in its trusted root store.
Why this is correct
SSL decryption makes the firewall re-sign traffic with its own CA. If that CA certificate is absent from the client's trusted root store, the browser cannot validate the forged certificate chain and raises a warning, even though decryption itself succeeds.
- ✗
The decryption policy is not matching the traffic because the destination is not specified.
Why it's wrong here
If the decryption policy failed to match, traffic would pass through undecrypted and the browser would see the server's genuine certificate, usually without warning. Destination matching is tempting because policy scope matters, but a non-matching rule produces no decryption rather than the certificate warning described.
- ✗
The firewall's decryption certificate is expired.
Why it's wrong here
An expired firewall decryption certificate produces warnings on every decrypted site, not one destination. It is tempting because expired certificates do cause browser warnings, but the scenario is site-specific, pointing to the forwarded server certificate chain rather than the firewall's own signing certificate used for outbound decryption.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCNSA practice question is part of Courseiva's free Palo Alto Networks 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 PCNSA exam.