Which network service is primarily responsible for authentication and authorization of VPN clients?

The reason RADIUS is the correct answer lies in its specific function in networking. RADIUS, which stands for Remote Authentication Dial-In User Service, is a protocol that provides centralized Authentication, Authorization, and Accounting (AAA) management for users who connect and use a network service. In the case of VPN clients, RADIUS enables the secure handling of authentication credentials, ensuring that only authorized users can access the VPN and, consequently, the network resources behind it.

When a user attempts to connect to a VPN, the request is sent to a RADIUS server, which authenticates the user's credentials (like username and password) and authorizes the user based on predefined policies. This process is critical for maintaining network security and integrity, especially in environments where remote access is common.

In contrast, LDAP (Lightweight Directory Access Protocol) is primarily used for directory services and may assist in authentication but does not handle the authorization and accounting aspects as effectively as RADIUS. FTP (File Transfer Protocol) is meant for transferring files and is not involved in user authentication for network access. DNS (Domain Name System) translates domain names into IP addresses and does not provide services for user authentication or authorization.

Thus, RADIUS stands out as the essential service for managing authentication and authorization