Here is a list of all the key features of Radius:
NAS works as a client for the Radius server.
Radius server is responsible for getting user connection requests, authenticating the user, and then returning all the configuration information necessary for the client to deliver service to the user.
A Radius server can act as a proxy client to other Radius servers.
Transactions between a client and a server are authenticated through the use of a shared key. This key is never sent over the network.
Password is encrypted before sending it over the network.
Radius supports the following protocols for authentication purpose:
Point-to-Point Protocal - PPP
Password Authentication Protocol - PAP
Challenge Handshake Authentication Protocol - CHAP
Simple UNIX Login
Radius is extensible; most vendors of Radius hardware and software implement their own dialects.
Stateless protocol, using UDP, runs at port 1812.