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 is implementing 802.1X port-based authentication on its wired network to ensure only authorized devices can connect. Which of the following servers is required to authenticate users and devices?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
A) RADIUS server
802.1X port-based authentication relies on the Extensible Authentication Protocol (EAP) over LAN (EAPoL) between the supplicant (device) and the authenticator (switch), which then forwards authentication requests to a central authentication server. A RADIUS server is the required backend because it validates credentials (e.g., username/password or certificates) and returns an Accept/Reject decision to the switch, enabling or disabling the port. RADIUS is the standard protocol defined in IEEE 802.1X for this purpose, supporting EAP methods like PEAP, EAP-TLS, and EAP-FAST.
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.
✓
A) RADIUS server
Why this is correct
Correct. RADIUS is the most common protocol for 802.1X authentication and is widely supported.
Related concept
Read the scenario before looking for a memorised answer.
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B) Syslog server
Why it's wrong here
Syslog servers collect log messages but do not perform authentication.
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C) TACACS+ server
Why it's wrong here
TACACS+ can be used for authentication, but RADIUS is the standard for 802.1X. Additionally, TACACS+ is proprietary to Cisco.
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D) NTP server
Why it's wrong here
NTP provides time synchronization, not authentication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that TACACS+ can replace RADIUS in 802.1X environments, but TACACS+ encrypts the entire packet body and is designed for device administration (e.g., CLI access), not for 802.1X port-based authentication, which mandates RADIUS per the IEEE 802.1X standard.
Detailed technical explanation
How to think about this question
Under the hood, the switch acts as an authenticator and encapsulates EAP frames from the supplicant into RADIUS Access-Request packets (using RADIUS attributes like User-Name and EAP-Message) and sends them to the RADIUS server. The RADIUS server processes the EAP conversation, often using a backend database (e.g., Active Directory or LDAP), and responds with Access-Accept (including attributes like Tunnel-Private-Group-ID for VLAN assignment) or Access-Reject. A subtle behavior is that if the RADIUS server is unreachable, the switch can fall back to a local authentication method (e.g., a local user database) if configured, but this is not part of the 802.1X standard.
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: A) RADIUS server — 802.1X port-based authentication relies on the Extensible Authentication Protocol (EAP) over LAN (EAPoL) between the supplicant (device) and the authenticator (switch), which then forwards authentication requests to a central authentication server. A RADIUS server is the required backend because it validates credentials (e.g., username/password or certificates) and returns an Accept/Reject decision to the switch, enabling or disabling the port. RADIUS is the standard protocol defined in IEEE 802.1X for this purpose, supporting EAP methods like PEAP, EAP-TLS, and EAP-FAST.
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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