RADIUS (Remote Authentication Dial In User Service)
RADIUS (Remote Authentication Dial In User Service) is an AAA (authentication, authorization and accounting) protocol for applications such as network access or IP mobility. It is intended to work in both local and roaming situations.
When you connect to an ISP using a modem, DSL, cable or wireless connection, you must enter your username and password. This information is passed to a Network Access Server (NAS) device over the Point-to-Point Protocol (PPP), then to a RADIUS server over the RADIUS protocol. The RADIUS server checks that the information is correct using authentication schemes like PAP, CHAP or EAP. If accepted, the server will then authorize access to the ISP system and select an IP address, L2TP parameters, etc.
The RADIUS server will also be notified when the session starts and stops, so that the user can be billed accordingly; or the data can be used for statistical purposes.