What protocol is recommended for implementing authentication in a VPN setup?

The correct choice for implementing authentication in a VPN setup is Remote Authentication Dial-in User Service (RADIUS). RADIUS is a network protocol that provides centralized Authentication, Authorization, and Accounting (AAA) management for users who connect and use a network service. Its design is particularly advantageous in a VPN context, where secure access to a network from remote locations is crucial.

When a user attempts to connect to a VPN, RADIUS serves to verify their credentials against a centralized database, ensuring that only authorized users gain access. This system enables administrators to efficiently manage user permissions and log connection history, which is essential for maintaining security and compliance standards.

While protocols like L2TP and IKE can be involved in VPN implementations, they are primarily focused on creating secure tunnels and negotiating keys rather than directly handling user authentication. SSL, on the other hand, primarily secures data transmission rather than performing user authentication in a VPN context. Thus, while these options play roles in VPN technology, RADIUS stands out specifically for its dedicated authentication capabilities.