The answer is a RADIUS server. This is required because 802.1X authentication relies on the Extensible Authentication Protocol (EAP) to secure port-based network access, and the RADIUS server acts as the backend that validates user credentials against an identity store while communicating with the network authenticator (such as a switch) via the RADIUS protocol defined in RFC 2865 and IEEE 802.1X-2020. On the Systems Security Practitioner SSCP exam, this concept tests your understanding of network access control (NAC) architecture, often appearing in questions about wired or wireless authentication flows. A common trap is confusing the authenticator (the switch or access point) with the authentication server, or assuming a directory service like LDAP alone suffices—but 802.1X mandates RADIUS as the intermediary that translates EAP frames. Remember the mnemonic: “RADIUS Rules the 802.1X Realm” to keep the server requirement clear.
SSCP Network and Communications Security Practice Question
This SSCP practice question tests your understanding of network and communications 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.
An organization is implementing 802.1X authentication for wired network access. Which server is required to authenticate users?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
RADIUS server
802.1X is a port-based network access control protocol that uses the Extensible Authentication Protocol (EAP) to authenticate devices before granting network access. The authentication server in an 802.1X deployment must be a RADIUS server, as defined in IEEE 802.1X-2020, because it acts as the backend that validates credentials and communicates with the authenticator (switch) via RADIUS (RFC 2865).
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.
✗
DHCP server
Why it's wrong here
DHCP assigns IP addresses but does not authenticate users for network access.
✗
TACACS+ server
Why it's wrong here
TACACS+ is primarily used for administrative access to network devices, not for 802.1X authentication.
✗
Kerberos server
Why it's wrong here
Kerberos is used for authentication in Windows domains but is not directly used in 802.1X (though it can be integrated with RADIUS).
✓
RADIUS server
Why this is correct
RADIUS is the standard authentication server for 802.1X, handling user credentials and policy enforcement.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse TACACS+ with RADIUS because both are AAA protocols, but 802.1X specifically mandates RADIUS for EAP transport, whereas TACACS+ encrypts the entire packet and is used for device administration, not port-based network access control.
Detailed technical explanation
How to think about this question
Under the hood, 802.1X uses a three-party architecture: the supplicant (client), the authenticator (switch), and the authentication server (RADIUS). The switch acts as a proxy, encapsulating EAP frames from the client into RADIUS Access-Request packets (RFC 3579) and forwarding them to the RADIUS server, which returns an Access-Accept or Access-Reject to control the port state. In real-world deployments, a RADIUS server like FreeRADIUS or Cisco ISE can integrate with LDAP or Active Directory for user lookup, but the core protocol exchange remains RADIUS.
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 analyst at a medium-sized enterprise encounters this scenario during an investigation or architecture review. The correct answer reflects best practice for the specific threat or control described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Security exam questions test whether you can match controls to threats in context — not just recall definitions.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Network and Communications Security — This question tests Network and Communications Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: RADIUS server — 802.1X is a port-based network access control protocol that uses the Extensible Authentication Protocol (EAP) to authenticate devices before granting network access. The authentication server in an 802.1X deployment must be a RADIUS server, as defined in IEEE 802.1X-2020, because it acts as the backend that validates credentials and communicates with the authenticator (switch) via RADIUS (RFC 2865).
What should I do if I get this SSCP 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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