What is the primary function of TACACS+, according to its design?

The primary function of TACACS+ (Terminal Access Controller Access-Control System Plus) is to perform AAA, which stands for authentication, authorization, and accounting, separately. TACACS+ is designed to provide a centralized way to manage user access to network resources while ensuring that each aspect of AAA can be handled independently. This separation is crucial for network administrators as it allows for more granular control over user permissions, enhances security management, and simplifies accountability.

Authentication verifies the identity of users trying to access the network, authorization determines what resources and actions the authenticated users are permitted to access and perform, and accounting tracks the activities of the users within the network. By facilitating this process in a distinct manner, TACACS+ enhances security and provides better management of user activities compared to systems that do not separate these functions.

While the other choices address important aspects of network security and data transfer, they do not reflect the primary purpose of TACACS+. Data encryption and assurance of data integrity can be part of its operation, but they're not its main focus. Tracking user permissions falls under the broader umbrella of authorization but does not encompass the full scope of what TACACS+ was designed to achieve in terms of AAA management.