This section will give you background on three common authentication protocols. These protocols involve the supply of a username and password.
The radtest program uses the Password Authentication Protocol (PAP) by default when testing authentication. PAP is not the only authentication protocol but probably the most generic and widely used. Authentication protocols you should know about are PAP, CHAP, and MS-CHAP. Each of these protocols involves a username and password. The Extensible Authentication Protocol (EAP) protocol has its own dedicated chapter later in this book and will introduce us to more authentication protocols.
An authentication protocol is typically used on the data link layer that connects the client with the NAS. The network layer will only be established after the authentication is successful. The NAS acts as a broker to forward the requests from the user to the RADIUS server.
Note
The data link layer and network layer are layers inside the Open...
