3Com Switch 7750 Configuration Guide Guide

464 CHAPTER 46: 802.1X CONFIGURATION
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 (alerting standards
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.
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 115.
Figure 115 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 does not contain the Data field, so has the Length field
of 4.
Figure 116 shows the Data field of Request and Response type packet.
Figure 116 Data fields
■ 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.
Code Identifier Length Data
0
12
4
N
Type Type Data