3Com Switch 4200G Configuration Guide

Introduction to 802.1x 151
■ EAP protocol packets transmitted between the supplicant system and the
authenticator system are encapsulated as EAPoL packets.
■ EAP protocol packets transmitted between the supplicant system PAE and the
RADIUS server can either be encapsulated as EAPoR (EAP over RADIUS) packets or
be terminated at system PAEs (The system PAEs then communicate with RADIUS
servers through PAP (password authentication protocol) or CHAP
(challenge-handshake authentication protocol) protocol packets.)
■ When a supplicant system passes the authentication, the authentication server
passes the information about the supplicant system to the authenticator system.
The authenticator system in turn determines the state (authorized or
unauthorized) of the controlled port according to the instructions (accept or reject)
received from the RADIUS server.
Encapsulation of EAPoL
Messages
The format of an EAPoL packet
EAPoL is a packet encapsulation format defined in 802.1x. To enable EAP protocol
packets to be transmitted between supplicant systems and authenticator systems
through LANs, EAP protocol packets are encapsulated in EAPoL format. Figure 45
illustrates the structure of an EAPoL packet.
Figure 45 The format of an EAPoL packet
In an EAPoL packet:
■ The PAE Ethernet type field holds the protocol identifier. The identifier for 802.1x is
888E.
■ The Protocol version field holds the version of the protocol supported by the
sender of the EAPoL packet.
■ The Type field can be one of the following:
00: Indicates that the packet is an EAP-packet, which carries authentication
information.
01: Indicates that the packet is an EAPoL-start packet, which initiates
authentication.
02: Indicates that the packet is an EAPoL-logoff packet, which sends logging off
requests.
03: Indicates that the packet is an EAPoL-key packet, which carries key
information packets.
04: Indicates that the packet is an EAPoL-encapsulated-ASF-Alert packet, which is
used to support the alerting messages of ASF (alert standard forum).
■ The Length field indicates the size of the Packet body field. A value of 0 indicates
that the Packet Body field does not exist.
■ The Packet body field differs with the Type field.
PAE Ethernet type Protocol version Length
0
2
3
4
Packet body
6N
TypePAE Ethernet type Protocol version Length
0
2
3
4
Packet body
6N
Type