Port security is the correct choice because it enables MAC address limiting on a switch port, allowing the administrator to define a specific list of allowed MAC addresses and restrict access to only those devices. When a device with an unauthorized MAC address attempts to connect, the switch can either block the traffic, generate an alert, or place the port into an errdisable state, enforcing strict access control at the data link layer. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of Layer 2 security features, often appearing in scenario-based questions where you must choose between port security, 802.1X, or DHCP snooping. A common trap is confusing port security with MAC filtering on a wireless network—remember that port security is a switch-port feature, not a wireless one. To recall the three violation modes, think of the mnemonic “S.P.A.”: Shutdown (errdisable), Protect (drops unknown frames), and Restrict (drops and logs).
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 administrator wants to ensure that only authorized devices can access the network on a switch port. The administrator has a list of allowed MAC addresses. Which security feature should be enabled on the switch port?
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 is the correct feature because it allows the administrator to specify a list of allowed MAC addresses per switch port. When a device with an unauthorized MAC address attempts to connect, the switch can either block the traffic, generate an alert, or disable the port (errdisable state). This directly enforces access control based on the MAC address list provided.
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.
✗
802.1X
Why it's wrong here
802.1X is an authentication protocol that requires user credentials, not just MAC address filtering.
Port security allows restricting access based on MAC addresses, preventing unauthorized devices.
Related concept
Read the scenario before looking for a memorised answer.
✗
VLAN hopping prevention
Why it's wrong here
VLAN hopping prevention protects against VLAN attacks, not device authorization.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between port security and MAC address filtering: candidates mistakenly choose 'MAC address filtering' because it sounds correct, but Cisco expects the exact feature name 'port security' as it is the configured command on a switch port.
Detailed technical explanation
How to think about this question
Port security uses the `switchport port-security` command and supports three violation modes: protect (drops traffic from unknown MACs), restrict (drops and logs), and shutdown (disables the port). The maximum number of secure MAC addresses defaults to 1 but can be increased, and sticky MAC learning can dynamically populate the allowed list. In a real-world scenario, an administrator might combine port security with 802.1X for multi-factor access control, but port security alone fulfills the requirement of a static MAC allow list.
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 help-desk technician troubleshoots why a newly connected PC cannot reach shared printers on the same floor. The cable is good, the switch port is active, but the PC is in VLAN 20 and the printers are in VLAN 10. The uplink trunk only allows VLAN 10. A trunk being up does not mean every VLAN crosses it.
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 is the correct feature because it allows the administrator to specify a list of allowed MAC addresses per switch port. When a device with an unauthorized MAC address attempts to connect, the switch can either block the traffic, generate an alert, or disable the port (errdisable state). This directly enforces access control based on the MAC address list provided.
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.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A network administrator wants to prevent unauthorized devices from being plugged into switch ports. Only devices with specific MAC addresses should be allowed on each port. Which switch security feature should be enabled?
easy
A.DHCP snooping
B.Dynamic ARP inspection
✓ C.Port security
D.802.1X
Why C: Port security is the correct feature because it allows the administrator to restrict which MAC addresses can communicate through a switch port. By configuring allowed MAC addresses (sticky or static), any device with an unknown MAC address attempting to send traffic will trigger a security violation (shutdown, restrict, or protect). This directly addresses the requirement to prevent unauthorized devices from being plugged into switch ports.
Variation 2. A network administrator wants to prevent unauthorized devices from connecting to the network by limiting the number of MAC addresses allowed on a switch port. Which security feature should be configured?
medium
A.802.1X
✓ B.Port security
C.DHCP snooping
D.Dynamic ARP inspection
Why B: Port security is the correct feature because it directly restricts the number of unique MAC addresses that can be learned on a switch port, preventing unauthorized devices from connecting. When the configured limit is exceeded, the switch can take actions such as shutdown, restrict, or protect, effectively blocking the unauthorized device. This is a Layer 2 access control mechanism that operates on the switch port itself.
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Question Discussion
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