Which protocol provides centralized authentication, authorization, and accounting for network access control?

• A. LDAP
• B. DNS
• C. HTTPS
• D. RADIUS

Answer: (D)

RADIUS provides centralized authentication, authorization, and accounting for network access control. It’s designed for network access scenarios where a client device like a wireless AP, VPN concentrator, or switch forwards a user’s credentials to a central server. The RADIUS server then authenticates the user, enforces policy-based authorization (determining what services or resources the user can access), and performs accounting by logging session start/stop, duration, and usage. This centralized AAA model simplifies enforcement and auditing across the network.

LDAP, while a directory service that can store and verify user credentials, is not itself a complete AAA solution for network access control and typically lacks the built-in accounting component. DNS and HTTPS serve different functions (name resolution and secure web transport, respectively) and do not provide centralized AAA for network access.