RADIUS - Overview
RADIUS is a protocol for carrying information related to authentication, authorization, and configuration between a Network Access Server that desires to authenticate its links and a shared Authentication Server.
RADIUS stands for Remote Authentication Dial In User Service.
RADIUS is an AAA protocol for applications such as Network Access or IP Mobility
It works in both situations, Local and Mobile.
It uses Password Authentication Protocol (PAP), Challenge Handshake Authentication Protocol (CHAP), or Extensible Authentication Protocol (EAP) protocols to authenticate users.
It look in text file, LDAP Servers, Database for authentication.
After authentication services parameters passed back to NAS.
It notifies when a session starts and stop. This data is used for Billing or Statistics purposes.
SNMP is used for remote monitoring.
It can be used as a proxy.
Here is a Simple Network Diagram of Radius: