- A
MAC filtering on the switch
Why wrong: MAC filtering allows only specific MAC addresses to access the network, but MAC addresses can be spoofed easily, so it is not a strong security measure.
- B
802.1X authentication
802.1X requires devices to authenticate (e.g., via username/password or certificates) before the switch port becomes active, effectively blocking unauthorized devices from accessing the network.
- C
VLAN segmentation
Why wrong: VLANs can limit the scope of malware spread by isolating traffic into separate networks, but they do not prevent an unauthorized device from connecting initially.
- D
Access control lists on the router
Why wrong: ACLs on a router can filter traffic based on IP addresses, but they do not prevent physical connection or initial link-layer access to the network.
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.
An employee plugs a personal laptop into a network jack and then the laptop is infected with malware that spreads to other devices on the network. Which security control would have most effectively prevented this scenario?
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
802.1X authentication
802.1X authentication requires devices to authenticate before gaining network access, typically via EAP (Extensible Authentication Protocol) over RADIUS. In this scenario, the employee's personal laptop would be blocked at the port level because it lacks valid credentials, preventing the malware from ever reaching the internal network and spreading to other devices.
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.
- ✗
MAC filtering on the switch
Why it's wrong here
MAC filtering allows only specific MAC addresses to access the network, but MAC addresses can be spoofed easily, so it is not a strong security measure.
- ✓
802.1X authentication
Why this is correct
802.1X requires devices to authenticate (e.g., via username/password or certificates) before the switch port becomes active, effectively blocking unauthorized devices from accessing the network.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
VLAN segmentation
Why it's wrong here
VLANs can limit the scope of malware spread by isolating traffic into separate networks, but they do not prevent an unauthorized device from connecting initially.
- ✗
Access control lists on the router
Why it's wrong here
ACLs on a router can filter traffic based on IP addresses, but they do not prevent physical connection or initial link-layer access to the network.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that MAC filtering or VLAN segmentation alone can prevent unauthorized device access, when in fact 802.1X is the only option that provides per-port authentication and dynamic VLAN assignment based on credentials.
Detailed technical explanation
How to think about this question
802.1X uses EAP over LAN (EAPoL) to exchange authentication messages between the supplicant (client), authenticator (switch), and authentication server (RADIUS). The switch places the port in an unauthorized state until authentication succeeds, blocking all traffic except EAPoL frames. In a real-world deployment, 802.1X can be combined with MAB (MAC Authentication Bypass) for legacy devices, but the core mechanism ensures that only authenticated endpoints gain Layer 2 access.
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
Got this wrong? Here's your next step.
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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: 802.1X authentication — 802.1X authentication requires devices to authenticate before gaining network access, typically via EAP (Extensible Authentication Protocol) over RADIUS. In this scenario, the employee's personal laptop would be blocked at the port level because it lacks valid credentials, preventing the malware from ever reaching the internal network and spreading to other devices.
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
This N10-009 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the N10-009 exam.
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