The correct answer is to clear the port security counters. When a switch port is configured with port security limiting access to a single MAC address, the switch locks onto the original laptop’s MAC address after it first connects. Replacing that laptop introduces a new MAC address, which the switch treats as a security violation because the port is already secured with the old address. Clearing the port security counters—using commands like `clear port-security sticky` or `clear port-security dynamic`—resets the learned MAC, allowing the switch to immediately learn the new device’s MAC on the next link-up. On the CISSP exam, this scenario tests your understanding of network access control and the operational nuance of port security remediation after device replacement; a common trap is to assume you must disable port security or reboot the switch. Remember the mnemonic “New MAC, Clear the Stack”—when a device is swapped, clear the counters to let the new address attach.
CISSP Communication and Network Security Practice Question
This CISSP practice question tests your understanding of communication and network security. 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.
A switch port is configured with port security that allows only one MAC address. The help desk reports that a user's device cannot connect after a laptop is replaced. What should the network administrator do to resolve the issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Clear the port security counters
When port security is configured to allow only one MAC address and a laptop is replaced, the new MAC address is automatically blocked because the switch has already learned and secured the old MAC address. Clearing the port security counters (e.g., using `clear port-security sticky` or `clear port-security dynamic`) resets the learned MAC address, allowing the switch to learn the new device's MAC address on the next link-up. This is the standard remediation without disabling security or causing unnecessary downtime.
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.
✓
Clear the port security counters
Why this is correct
Clearing the counters removes the existing MAC address, allowing the new one to be learned.
Related concept
Read the scenario before looking for a memorised answer.
✗
Disable port security
Why it's wrong here
Disabling port security removes the protection entirely.
✗
Shut down the port and re-enable
Why it's wrong here
This may not clear the learned MAC; it only resets the link.
✗
Change the port security to sticky MAC
Why it's wrong here
Sticky MAC converts dynamically learned addresses to static, not resolving the current issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
ISC2 often tests the misconception that simply bouncing the port (shut/no shut) will fix the issue, but candidates forget that the learned MAC address persists in the secure MAC table until explicitly cleared, so the port remains in violation even after re-enabling.
Detailed technical explanation
How to think about this question
Port security uses a violation mode (shutdown, restrict, or protect) to handle unauthorized MAC addresses; the default is shutdown, which error-disables the port. Clearing the counters (via `clear port-security dynamic` or `clear port-security sticky`) removes the dynamically learned MAC address from the secure MAC address table, allowing the switch to re-learn the new MAC on the next frame. In Cisco IOS, the `errdisable recovery` feature can automate this, but manual intervention is often required in exam scenarios.
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 security team runs a vulnerability scan on a web application and discovers an unpatched SQL injection flaw. The team prioritises remediation by CVSS score — critical flaws are patched within 24 hours, high within 7 days. Questions like this test whether you understand vulnerability management processes, scanning tools, and remediation prioritisation.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this CISSP question in full detail.
Communication and Network Security — This question tests Communication and Network Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Clear the port security counters — When port security is configured to allow only one MAC address and a laptop is replaced, the new MAC address is automatically blocked because the switch has already learned and secured the old MAC address. Clearing the port security counters (e.g., using `clear port-security sticky` or `clear port-security dynamic`) resets the learned MAC address, allowing the switch to learn the new device's MAC address on the next link-up. This is the standard remediation without disabling security or causing unnecessary downtime.
What should I do if I get this CISSP question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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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