- A
802.1X authentication
Why wrong: 802.1X uses usernames/passwords or certificates for authentication, not MAC addresses. While it can be integrated with MAC authentication bypass, the question specifically asks for MAC-based restriction.
- B
MAC filtering / Port security
Port security (MAC filtering) allows an administrator to define a list of allowed MAC addresses on a switch port. Any device with a MAC not on the list is blocked from sending traffic.
- C
VLAN hopping prevention
Why wrong: VLAN hopping prevention techniques (e.g., disabling DTP, setting native VLAN to unused) protect against attacks that attempt to access other VLANs, not against unauthorized device connections.
- D
DHCP snooping
Why wrong: DHCP snooping prevents rogue DHCP servers and maintains a binding table of IP-MAC addresses. It does not directly restrict which MAC addresses can connect to a port.
Quick Answer
The answer is MAC filtering, also known as port security, because it directly restricts which devices can connect to a switch port by checking the source MAC address of every incoming frame against a configured list of allowed addresses. This feature enforces the policy that only specific MAC addresses are permitted, dropping traffic from any unauthorized device at the port level. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of Layer 2 access control, often appearing in questions about preventing rogue devices or securing physical ports. A common trap is confusing MAC filtering with 802.1X authentication—while both control access, port security is statically configured on the switch itself, whereas 802.1X relies on a RADIUS server. Remember the memory tip: “MAC filtering is a static bouncer at the door; 802.1X is a dynamic ID check with a central database.”
N10-009 Network Security Practice Question
This N10-009 practice question tests your understanding of network security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 wants to prevent unauthorized devices from connecting to the corporate network. The policy requires that only specific MAC addresses are permitted on switch ports. Which security feature should be implemented on the switches?
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
MAC filtering / Port security
MAC filtering, also known as port security, is the correct feature because it allows the switch to restrict access to a port based on the source MAC address of incoming frames. By configuring a list of allowed MAC addresses, the switch will drop traffic from any unauthorized device, directly enforcing the policy that only specific MAC addresses are permitted on switch 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.
- ✗
802.1X authentication
Why it's wrong here
802.1X uses usernames/passwords or certificates for authentication, not MAC addresses. While it can be integrated with MAC authentication bypass, the question specifically asks for MAC-based restriction.
- ✓
MAC filtering / Port security
Why this is correct
Port security (MAC filtering) allows an administrator to define a list of allowed MAC addresses on a switch port. Any device with a MAC not on the list is blocked from sending traffic.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
VLAN hopping prevention
Why it's wrong here
VLAN hopping prevention techniques (e.g., disabling DTP, setting native VLAN to unused) protect against attacks that attempt to access other VLANs, not against unauthorized device connections.
- ✗
DHCP snooping
Why it's wrong here
DHCP snooping prevents rogue DHCP servers and maintains a binding table of IP-MAC addresses. It does not directly restrict which MAC addresses can connect to a port.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between MAC-based port security and 802.1X authentication, where candidates mistakenly choose 802.1X because it is a more robust access control method, but the question specifically asks for a feature that permits only specific MAC addresses, which is exactly what port security does.
Detailed technical explanation
How to think about this question
Port security works by learning MAC addresses on a switch port and comparing them against a configured list of allowed addresses (sticky MAC addresses can be used to dynamically learn and lock addresses). If a violation occurs (e.g., an unknown MAC address attempts to send traffic), the switch can take actions such as shutting down the port (errdisable state), dropping the offending frames, or generating a syslog message. In a real-world scenario, an attacker could spoof a permitted MAC address to bypass port security, so it is often combined with 802.1X for stronger authentication.
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.
What to study next
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FAQ
Questions learners often ask
What does this N10-009 question test?
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: MAC filtering / Port security — MAC filtering, also known as port security, is the correct feature because it allows the switch to restrict access to a port based on the source MAC address of incoming frames. By configuring a list of allowed MAC addresses, the switch will drop traffic from any unauthorized device, directly enforcing the policy that only specific MAC addresses are permitted on switch 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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Last reviewed: Jun 11, 2026
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