The answer is 802.1X, the IEEE standard for port-based Network Access Control (NAC) that should be implemented at the switch level. When a device plugs into a network jack, the switch acts as an authenticator and blocks all traffic except Extensible Authentication Protocol over LAN (EAPoL) frames until the device authenticates with a RADIUS server, effectively preventing unauthorized wired network access. On the CompTIA Network+ N10-009 exam, this concept tests your understanding of how to secure physical ports against rogue connections; a common trap is confusing 802.1X with MAC filtering, which only checks hardware addresses and can be spoofed. Remember that 802.1X uses a three-party model—supplicant, authenticator, and authentication server—so think “port lockdown before handshake.” A helpful memory tip: “X marks the spot, but only after the RADIUS handshake unlocks the port.”
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 company wants to prevent unauthorized users from plugging into network jacks and gaining access to the wired network. Which of the following security mechanisms should be implemented at the switch level?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
802.1X
802.1X is a port-based Network Access Control (NAC) standard (IEEE 802.1X) that authenticates devices before granting full network access. When a device plugs into a switch port, the switch (as the authenticator) blocks all traffic except EAPoL (Extensible Authentication Protocol over LAN) frames until the device successfully authenticates via a RADIUS server. This prevents unauthorized users from gaining network access simply by connecting to a live jack.
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 address filtering
Why it's wrong here
MAC filtering can be bypassed by MAC spoofing and is not a strong authentication method.
✗
Port security
Why it's wrong here
Port security limits the number of MAC addresses per port, but it does not authenticate users and can be circumvented.
✓
802.1X
Why this is correct
802.1X requires user or device authentication via an authentication server (RADIUS) before the switch port becomes active.
Related concept
Read the scenario before looking for a memorised answer.
✗
Dynamic ARP Inspection
Why it's wrong here
DAI prevents ARP spoofing attacks, but it does not control initial network access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse port security (which only limits MAC addresses) with 802.1X (which provides actual authentication), leading them to pick port security because it sounds like it 'secures the port' at the switch level.
Detailed technical explanation
How to think about this question
802.1X uses three roles: supplicant (client), authenticator (switch), and authentication server (RADIUS). The switch places the port in an unauthorized state, allowing only 802.1X EAPoL frames (EtherType 0x888E) to pass. After successful authentication, the switch dynamically opens the port, often applying a specific VLAN or ACL based on RADIUS attributes. A common real-world scenario is a conference room jack where 802.1X ensures only corporate devices with valid certificates or credentials can connect, while guests are redirected to a captive portal or isolated VLAN.
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 junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
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: 802.1X — 802.1X is a port-based Network Access Control (NAC) standard (IEEE 802.1X) that authenticates devices before granting full network access. When a device plugs into a switch port, the switch (as the authenticator) blocks all traffic except EAPoL (Extensible Authentication Protocol over LAN) frames until the device successfully authenticates via a RADIUS server. This prevents unauthorized users from gaining network access simply by connecting to a live jack.
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
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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. 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?
medium
A.MAC filtering on the switch
✓ B.802.1X authentication
C.VLAN segmentation
D.Access control lists on the router
Why B: 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.
Last reviewed: Jun 11, 2026
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