The answer is port security. This feature mitigates MAC address table overflow attacks by limiting the number of unique source MAC addresses that can be learned on a switch access port, preventing an attacker from flooding the CAM table with fake entries. When that limit is exceeded, the switch can be configured to shut down the port or restrict traffic, stopping the switch from failing open and flooding unicast frames out all ports—the classic symptom of a MAC address table overflow attack. On the CompTIA Network+ N10-009 exam, this scenario tests your understanding of how Layer 2 attacks exploit switch behavior and the specific countermeasure designed to protect the MAC address table. A common trap is confusing port security with DHCP snooping or dynamic ARP inspection, but remember: port security directly controls MAC address learning, not IP or ARP validation. For a quick memory tip, think “port security = MAC limit = no flood.”
N10-009 Network Security Practice Question
This N10-009 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 network security analyst notices that a switch's CPU utilization is spiking and that the switch is flooding unicast frames to all ports. The analyst suspects a MAC address table overflow attack. Which of the following security features should be configured on the switch's access ports to mitigate this type of attack?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Port security
Port security mitigates MAC address table overflow attacks by limiting the number of MAC addresses that can be learned on an access port. When the configured limit is exceeded, the switch can take action (e.g., shutdown or restrict) to prevent an attacker from flooding the CAM table with fake source MAC addresses, which would otherwise cause the switch to fail open and flood unicast frames out all ports.
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.
✗
BPDU guard
Why it's wrong here
BPDU guard protects against STP manipulation, not against MAC flooding.
✓
Port security
Why this is correct
Port security limits the number of MAC addresses per port, directly mitigating MAC flooding attacks.
Related concept
Read the scenario before looking for a memorised answer.
✗
DHCP snooping
Why it's wrong here
DHCP snooping prevents rogue DHCP servers but does not prevent MAC flooding.
✗
Dynamic ARP Inspection (DAI)
Why it's wrong here
DAI verifies ARP packets against DHCP snooping bindings and prevents ARP spoofing, not MAC flooding.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse port security with other Layer 2 security features like BPDU guard or DHCP snooping, but only port security directly limits the number of MAC addresses learned on a port to prevent CAM table overflow.
Detailed technical explanation
How to think about this question
Under the hood, a MAC address table overflow attack exploits the switch's limited Content Addressable Memory (CAM) table size; once full, the switch enters a fail-open state where it floods all unknown unicast frames out every port, effectively turning it into a hub. Port security counters this by enforcing a per-port MAC address limit (e.g., 'switchport port-security maximum 1'), and when exceeded, the port can be err-disabled or drop traffic, preserving the CAM table integrity. In a real-world scenario, an attacker on an access port could use a tool like macof to generate thousands of random source MAC addresses, causing network-wide flooding and potential eavesdropping.
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 N10-009 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this N10-009 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: Port security — Port security mitigates MAC address table overflow attacks by limiting the number of MAC addresses that can be learned on an access port. When the configured limit is exceeded, the switch can take action (e.g., shutdown or restrict) to prevent an attacker from flooding the CAM table with fake source MAC addresses, which would otherwise cause the switch to fail open and flood unicast frames out all ports.
What should I do if I get this N10-009 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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