Remote Authentication Dial-In User Service (RADIUS) is a client-server networking protocol that safeguards networks against unauthorized access. Along with a RADIUS Client or Network Access Server (NAS), that is used to authenticate users, and a RADIUS Server that runs on a UNIX or Windows server, that maintains user profiles in a central database, you have control over who can connect with your network.
When you configure Network Policy Server (NPS server) as a RADIUS proxy, to authenticate, authorize, and account (AAA) server groups, it offers a way to select a group of the configured server hosts and use them for a specific service.