- A
A) RADIUS server
Correct. RADIUS is the most common protocol for 802.1X authentication and is widely supported.
- B
B) Syslog server
Why wrong: Syslog servers collect log messages but do not perform authentication.
- C
C) TACACS+ server
Why wrong: TACACS+ can be used for authentication, but RADIUS is the standard for 802.1X. Additionally, TACACS+ is proprietary to Cisco.
- D
D) NTP server
Why wrong: NTP provides time synchronization, not authentication.
Question 66 of 520
802.1X RADIUS Server Requirement
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 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
✓
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
- ✗
B) Syslog server
Why it's wrong here
Syslog servers collect log messages but do not perform authentication.
- ✗
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.
When this WOULD be correct
A question asks: 'Which server is used to authenticate network administrators when they log into routers and switches?' In that context, TACACS+ would be the correct answer because it separates authentication, authorization, and accounting for device administration.
- ✗
D) NTP server
Why it's wrong here
NTP provides time synchronization, not authentication.
When this WOULD be correct
A question asking which server ensures accurate timestamps for logs or certificate validation in a PKI environment would have NTP as the correct answer. For example: 'A company needs to synchronize clocks for log correlation and certificate validity checks. Which server is required?'
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The N10-009 exam frequently reuses these exact scenarios with slightly different constraints.
✓A) RADIUS serverCorrect answer▾
Why this is correct
Correct. RADIUS is the most common protocol for 802.1X authentication and is widely supported.
✗C) TACACS+ serverWrong answer — click to see why▾
Why this is wrong here
TACACS+ is used for device administration authentication (e.g., router/switch login), not for 802.1X port-based network access control. 802.1X requires a RADIUS server to authenticate users and devices connecting to the network.
★ When this WOULD be the correct answer
A question asks: 'Which server is used to authenticate network administrators when they log into routers and switches?' In that context, TACACS+ would be the correct answer because it separates authentication, authorization, and accounting for device administration.
Why candidates choose this
Candidates confuse TACACS+ with RADIUS because both are AAA protocols. They may think TACACS+ can also handle network access authentication, but 802.1X specifically requires RADIUS.
✗D) NTP serverWrong answer — click to see why▾
Why this is wrong here
NTP (Network Time Protocol) servers synchronize clocks across network devices, but they do not perform authentication of users or devices. 802.1X requires a RADIUS server to validate credentials and authorize access.
★ When this WOULD be the correct answer
A question asking which server ensures accurate timestamps for logs or certificate validation in a PKI environment would have NTP as the correct answer. For example: 'A company needs to synchronize clocks for log correlation and certificate validity checks. Which server is required?'
Why candidates choose this
Candidates may confuse NTP with authentication servers because time synchronization is critical for Kerberos and certificate-based authentication, leading them to incorrectly assume NTP is part of the 802.1X authentication process.
Analysis generated from the official N10-009blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The N10-009 exam 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.
Quick reference
AAA Protocol Comparison
| Protocol | Port(s) | Encryption | Transport | Primary Use |
|---|---|---|---|---|
| RADIUS | 1812 / 1813 | Password only | UDP | Network access control |
| TACACS+ | 49 | Full packet | TCP | Device administration |
| Diameter | 3868 | Full session | TCP / SCTP | Carrier / mobile networks |
| 802.1X | — | EAP-based | Layer 2 | Port-based access control |
TACACS+ encrypts the entire packet; RADIUS only encrypts the password field — a key exam distinction.
What to study next
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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: 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.
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 →
Same concept, more angles
1 more ways this is tested on N10-009
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. A company is implementing 802.1X port-based authentication on its wired network to control access. The network uses Active Directory for user accounts. Which type of server must be deployed to authenticate clients connecting to the switch ports?
hard- A.A DNS server
- B.A DHCP server
- ✓ C.A RADIUS server
- D.A Kerberos server
Why C: 802.1X port-based authentication requires a RADIUS server to act as the authentication server that validates client credentials against the identity store (Active Directory). The switch (authenticator) forwards EAP frames from the client (supplicant) to the RADIUS server, which checks the credentials and instructs the switch to grant or deny port access.
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Last reviewed: Jun 11, 2026
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