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.
Which of the following security mechanisms requires a user to authenticate before gaining access to the wired network at a switch port?
802.1X is a Layer 2 protocol that blocks all traffic until the device authenticates, providing strong access control.
B
Port security
Why wrong: Port security limits based on MAC addresses but does not require authentication; MAC addresses can be spoofed.
C
ACL
Why wrong: Access control lists filter traffic after the connection is established, they do not authenticate the user before access.
D
MAC authentication
Why wrong: MAC authentication is a form of authentication based on the MAC address, but it is less secure than 802.1X and can be bypassed. 802.1X is the more robust standard.
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 requires a user or device to authenticate via an authentication server (e.g., RADIUS) before the switch port transitions from an unauthorized to an authorized state, allowing full network access. It uses Extensible Authentication Protocol (EAP) over LAN (EAPoL) to carry authentication messages between the supplicant (client), authenticator (switch), and authentication server. This ensures that only authenticated users can access the wired network at the switch port level.
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 this is correct
802.1X is a Layer 2 protocol that blocks all traffic until the device authenticates, providing strong access control.
Related concept
Read the scenario before looking for a memorised answer.
✗
Port security
Why it's wrong here
Port security limits based on MAC addresses but does not require authentication; MAC addresses can be spoofed.
✗
ACL
Why it's wrong here
Access control lists filter traffic after the connection is established, they do not authenticate the user before access.
✗
MAC authentication
Why it's wrong here
MAC authentication is a form of authentication based on the MAC address, but it is less secure than 802.1X and can be bypassed. 802.1X is the more robust standard.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between 802.1X (user authentication) and port security (MAC address filtering), leading candidates to confuse MAC-based restrictions with true authentication mechanisms.
Detailed technical explanation
How to think about this question
Under the hood, 802.1X uses a three-party architecture: the supplicant (client software), the authenticator (switch), and the authentication server (typically a RADIUS server). The switch initially places the port in an unauthorized state, allowing only EAPoL frames; upon successful authentication, the switch dynamically opens the port for all traffic. A subtle behavior is that 802.1X can be combined with MAB (MAC Authentication Bypass) as a fallback for devices that do not support 802.1X, but this reduces security to MAC-based control.
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 security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
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 requires a user or device to authenticate via an authentication server (e.g., RADIUS) before the switch port transitions from an unauthorized to an authorized state, allowing full network access. It uses Extensible Authentication Protocol (EAP) over LAN (EAPoL) to carry authentication messages between the supplicant (client), authenticator (switch), and authentication server. This ensures that only authenticated users can access the wired network at the switch port level.
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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