Which protocol is designed to provide authentication, authorization, and accounting for remote-access servers?

The choice of Radius as the correct answer is based on its primary function in network security. RADIUS, which stands for Remote Authentication Dial-In User Service, is a networking protocol specifically designed to provide centralized Authentication, Authorization, and Accounting (AAA) management for users accessing a network.

In this context, when users attempt to connect to a remote-access server, the RADIUS protocol authenticates their credentials, determines what level of access they have (authorization), and keeps records of their activities for accounting purposes. It is widely used in environments where secure remote access is needed, such as enterprise networks and service providers, making it critical for managing user access.

The other options do not serve this specific purpose. Simple Network Management Protocol (SNMP) is primarily used for network management and monitoring devices, not for user authentication or authorization. Internet Protocol Security (IPSec) is a framework used to secure Internet Protocol communications through encryption and is not directly involved in user management processes. Hypertext Transfer Protocol (HTTP) is a protocol for transmitting hypertext via the web and does not provide AAA services at all.

Thus, Radius is correctly identified as the protocol focused specifically on providing authentication, authorization, and accounting for remote-access services.