1-403: 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 supportthe 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 PacketBody field does not exist.z The Packet body field differs with the Type field.Note that EAPoL-Start, EAPoL-Logoff, and EAPoL-Key packets are only transmitted between thesupplicant system and the authenticator system. EAP-packets are encapsulated by RADIUS protocol toallow them successfully reach the authentication servers. Network management-related information(such as alarming information) is encapsulated in EAPoL-Encapsulated-ASF-Alert packets, which areterminated by authenticator systems.The format of an EAP packetFor an EAPoL packet with the value of the Type field being EAP-packet, its Packet body field is an EAPpacket, whose format is illustrated in Figure 1-4.Figure 1-4 The format of an EAP packetIn an EAP packet:z The Code field indicates the EAP packet type, which can be Request, Response, Success, orFailure.z The Identifier field is used to match a Response packet with the corresponding Request packet.z The Length field indicates the size of an EAP packet, which includes the Code, Identifier, Length,and Data fields.z The Data field carries the EAP packet, whose format differs with the Code field.A Success or Failure packet does not contain the Data field, so the Length field of it is 4.Figure 1-5 shows the format of the Data field of a Request packet or a Response packet.Figure 1-5 The format of the Data field of a Request packet or a Response packetz The Type field indicates the EAP authentication type. A value of 1 indicates Identity and that thepacket is used to query the identity of the peer. A value of 4 represents MD5-Challenge (similar toPPP CHAP) and indicates that the packet includes query information.z The Type Date field differs with types of Request and Response packets.
