EAP

Most enterprises want to do more for security than simply employing usernames and passwords for access, so a new authentication protocol, called the Extensible Authentication Protocol (EAP), was designed to supplement PPP.

EAP sits inside of PPP's authentication protocol and provides a generalized framework for several different authentication methods. EAP is supposed to head off proprietary authentication systems and let everything from passwords to challenge-response tokens and public-key infrastructure certificates all work smoothly.

With a standardized EAP, interoperability and compatibility of authentication methods becomes simpler. For example, when you dial a remote-access server and use EAP as part of your PPP connection, the RAS doesn't need to know any of the details about your authentication system. Only you and the authentication server have to be coordinated. By supporting EAP authentication a RAS server gets out of the business of acting as middle man, and just packages and repackages EAP packets to hand off to a RADIUS server that will do the actual authentication.

From What is 802.1x? Network World, 05/06/02.

Also see 802.1X.