1-3
Figure 1-2 The mechanism of an 802.1x authentication system
z EAP protocol packets transmitted between the supplicant system PAE and the authenticator
system PAE are encapsulated as EAPoL packets.
z EAP protocol packets transmitted between the authenticator system PAE and the RADIUS server
can either be encapsulated as EAP over RADIUS (EAPoR) packets or be terminated at system
PAEs. The system PAEs then communicate with RADIUS servers through password
authentication protocol (PAP) or challenge-handshake authentication protocol (CHAP) packets.
z 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. The following figure illustrates the structure of an EAPoL
packet.
Figure 1-3 The format of an EAPoL packet
In an EAPoL packet:
z The PAE Ethernet type field holds the protocol identifier. The identifier for 802.1x is 0x888E.
z The Protocol version field holds the version of the protocol supported by the sender of the EAPoL
packet.
z 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 the 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.
04: Indicates that the packet is an EAPoL-encapsulated-ASF-Alert packet, which is used to
support the alerting messages of ASF (alerting standards forum).
z The Length field indicates the size of the Packet body field. A value of 0 indicates that the Packet
Body field does not exist.
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