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 ensure that only users who have successfully authenticated Active Directory credentials can access the wired network. The network switches support IEEE 802.1X. Which additional component must be deployed to complete the solution?
RADIUS is the standard authentication server used with 802.1X to validate credentials against an identity source like Active Directory.
B
A DHCP server
Why wrong: DHCP provides IP addresses but does not handle authentication; it is used after the client is granted access.
C
A certificate authority
Why wrong: While certificates can be used with EAP-TLS, they are not required for all 802.1X implementations; a RADIUS server is the essential component.
D
A TACACS+ server
Why wrong: TACACS+ is typically used for administrative access to network devices, not for end-user network authentication via 802.1X.
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
IEEE 802.1X port-based authentication requires a RADIUS server to act as the authentication server. The switch (authenticator) forwards the user's credentials to the RADIUS server, which validates them against Active Directory and returns an accept or reject decision. Without a RADIUS server, the switch has no way to verify the user's credentials against the central identity store.
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
RADIUS is the standard authentication server used with 802.1X to validate credentials against an identity source like Active Directory.
Related concept
Read the scenario before looking for a memorised answer.
✗
A DHCP server
Why it's wrong here
DHCP provides IP addresses but does not handle authentication; it is used after the client is granted access.
✗
A certificate authority
Why it's wrong here
While certificates can be used with EAP-TLS, they are not required for all 802.1X implementations; a RADIUS server is the essential component.
✗
A TACACS+ server
Why it's wrong here
TACACS+ is typically used for administrative access to network devices, not for end-user network authentication via 802.1X.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between RADIUS (for network access) and TACACS+ (for device administration), leading candidates to mistakenly choose TACACS+ because it is associated with authentication, even though 802.1X specifically requires RADIUS.
Detailed technical explanation
How to think about this question
In an 802.1X deployment, the switch acts as the authenticator and uses RADIUS (RFC 2865) to communicate with the authentication server. The RADIUS server typically integrates with Active Directory via LDAP or Kerberos to validate credentials. A common subtlety is that the RADIUS server must be configured with the correct shared secret and must support the EAP method used by the client (e.g., PEAP or EAP-TTLS) to securely tunnel the credential exchange.
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 — IEEE 802.1X port-based authentication requires a RADIUS server to act as the authentication server. The switch (authenticator) forwards the user's credentials to the RADIUS server, which validates them against Active Directory and returns an accept or reject decision. Without a RADIUS server, the switch has no way to verify the user's credentials against the central identity store.
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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