Extensible Authentication Protocol (EAP)

Extensible Authentication Protocol (EAP) provides a message format for use by different types of authentication mechanisms. The EAP header itself is quite simple:

• Code - 8 bits
• Identifier - 8 bits
• Length - 16 bits

There are four codes defined:

1. Request
2. Response
3. Success
4. Failure

In the cases of request or response, an additional 8-bit Type field occurs next, followed by whatever data is specific to the type. The ability to define new types is what makes EAP extensible. Types defined in RFC 3748 include:

• Type 4 - MD5 Challenge
• Type 5 - One Time Password
• Type 6 - Generic Token Card

Other types and methods are also available.

With respect to the transmission of request-response traffic, EAP supports both peer-to-peer and pass-through models. For an example of pass-through, see 802.1X.

Reference: http://www.networksorcery.com/enp/protocol/eap.htm