The answer is that the switch firmware update caused it to present a different certificate not trusted by the clients, leading to 802.1X PEAP certificate authentication failure. This is correct because PEAP-MSCHAPv2 requires the client to validate the RADIUS server’s certificate against its trusted root store; the error “Unknown CA certificate” explicitly means the client cannot verify the certificate’s issuing authority. On the ISC2 Certified in Cybersecurity CC exam, this scenario tests your understanding of how certificate trust chains affect network authentication—a common trap is blaming the client’s credentials or the switch’s physical ports, but the real issue is the server certificate mismatch after the update. Remember that in PEAP, the “P” stands for Protected, meaning the client must first trust the server’s identity before exchanging credentials. Memory tip: “PEAP first checks the CA, not the password.”
ISC2 CC Network Security Practice Question
This CC practice question tests your understanding of network security. 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.
A company's network uses 802.1X authentication with PEAP-MSCHAPv2 on wired ports. Users report that after a recent switch firmware update, some workstations fail to authenticate intermittently, while others work fine. The authentication server logs show 'Authentication failed: Unknown CA certificate' for affected workstations. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The switch is now using a different certificate that is not trusted by the clients
The error 'Unknown CA certificate' indicates that the client does not trust the certificate presented by the RADIUS server during PEAP-MSCHAPv2 authentication. After a switch firmware update, the switch may have been reconfigured to use a different server certificate (e.g., a self-signed or internally issued certificate) that is not in the trusted root store of the affected workstations. Since PEAP requires the client to validate the server certificate, a mismatch causes intermittent authentication failures.
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 switch is now using a different certificate that is not trusted by the clients
Why this is correct
The firmware update may have changed the certificate presented by the switch, and clients do not trust it.
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 switch is not forwarding EAP packets properly due to a firmware bug
Why it's wrong here
The error message indicates a certificate issue, not packet forwarding.
✗
The RADIUS shared secret was changed during the firmware update
Why it's wrong here
A shared secret mismatch would cause 'Access-Reject' or 'Authentication failed' without certificate-specific errors.
✗
The authentication server (NPS) is overloaded and dropping requests
Why it's wrong here
Overload would cause timeouts, not certificate errors.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the distinction between authentication failures caused by certificate trust issues versus RADIUS shared secret mismatches, trapping candidates who confuse server-side RADIUS configuration with client-side certificate validation.
Detailed technical explanation
How to think about this question
PEAP-MSCHAPv2 creates a TLS tunnel between the client and the RADIUS server; the client must validate the server's certificate against its trusted root store. If the switch (acting as the authenticator) is configured to proxy EAP packets to a RADIUS server that presents a certificate from a CA not trusted by the client, the client will reject the tunnel. In some switch firmware updates, the default certificate or trust anchor may change, causing previously working clients to fail if they lack the updated CA certificate.
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 developer is choosing between AES-256 (symmetric) and RSA-2048 (asymmetric) for encrypting a large file that will be sent to a partner. Symmetric encryption is fast but requires key exchange; asymmetric is slower but solves the key distribution problem. A hybrid approach — encrypt the file with AES, encrypt the AES key with RSA — is standard. Questions like this test whether you understand when each approach applies.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CC question in full detail.
Network Security — This question tests Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The switch is now using a different certificate that is not trusted by the clients — The error 'Unknown CA certificate' indicates that the client does not trust the certificate presented by the RADIUS server during PEAP-MSCHAPv2 authentication. After a switch firmware update, the switch may have been reconfigured to use a different server certificate (e.g., a self-signed or internally issued certificate) that is not in the trusted root store of the affected workstations. Since PEAP requires the client to validate the server certificate, a mismatch causes intermittent authentication failures.
What should I do if I get this CC 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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