3Com Switch 4200G Configuration Guide

152 CHAPTER 21: 802.1X CONFIGURATION

Note that EAPoL-Start, EAPoL-Logoff, and EAPoL-Key packets are only transmitted

between the supplicant system and the authenticator system. EAP-packets are

encapsulated by RADIUS protocol to allow them successfully reach the authentication

servers. Network management-related information (such as alarming information) is

encapsulated in EAPoL-Encapsulated-ASF-Alert packets, which are terminated by

authenticator systems.

The format of an EAP packet

For an EAPoL packet with the Type value being EAP-packet, the corresponding Packet

body is an EAP packet. Its format is illustrated in Figure 46.

Figure 46 The format of an EAP packet

In an EAP packet:

■ The Code field specifies the EAP packet type, which can be Request, Response,

Success, or Failure.

■ The Identifier field is used to match a Response packets with the corresponding

Request packet.

■ The Length field indicates the size of an EAP packet, which includes the Code,

Identifier, Length, and Data fields.

■ The Data field differs with the Code field.

A Success or Failure packet, whose format is shown in Figure 47, does not contain the

Data field, so has the Length field of 4.

Figure 47 Data fields

In a Success or Failure packet, the Type field specifies the EAP authentication type. A

Type value of 1 indicates Identity and that the packet is used to query the identity of

the peer. A type value of 4 represents MD5-Challenge (similar to PPP CHAP) and

indicates that the packet includes query information.

Newly added fields for EAP authentication

Two fields, EAP-message and Message-authenticator, are added to a RADIUS protocol

packet for EAP authentication. (Refer to the Introduction to RADIUS protocol section

in the AAA and RADIUS Operation Manual for format of a RADIUS protocol packet.)

The EAP-message field, shown in Figure 48, is used to encapsulate EAP packets. The

maximum size of the string field is 253 bytes. EAP packets with their size larger than

253 bytes are fragmented and stored in multiple EAP-message fields. The type code

of the EAP-message field is 79.

Code Identifier Length Data

0124

Type Type Data