RADIUS

RADIUS stands for Remote Authentication Dial in User Service. It is used to
authenticate remote users. Instead of authenticating users at individual RAS server, we
pass a request to central server (RADIUS server), and let the authentication happen there.
All RAS servers pass authentication requests to this central server (RADIUS server) that
is doing the authentication. It is authenticating users based on Active Directory. It is also
doing reporting, so it is doing .accounting and authentication. With RADIUS
authentication will takes place at a central location. Now there is no need to maintain a
local database of users for each RAS server. When ever authentication needed RAS
server forwards query to RADIUS server.
Accounting means we keep tracking who is connected, how long, why they failed to
connect etc., the information is all centralized here.