Which protocol allows an authentication server to authenticate user accounts and other user information?

The best choice for a protocol that allows an authentication server to authenticate user accounts and other user information is RADIUS, which stands for Remote Authentication Dial-In User Service. RADIUS serves as a centralized authentication mechanism, allowing organizations to manage user credentials and permissions consistently across various network devices and services.

RADIUS operates over UDP and combines authentication, authorization, and accounting (AAA) for users who connect and use a network service. It facilitates secure communication between a client (like a network access server) and an authentication server, making it essential for environments that require robust access control, such as corporate networks or VPNs.

While other options like LDAP (Lightweight Directory Access Protocol) also relate to user authentication and directory services, RADIUS specifically focuses on the AAA services needed for user authentication. This highlights RADIUS's primary role in managing access control across varying network types, especially for remote access, making it a critical choice in network security scenarios.