1-4
z
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 value of the Type field being EAP-packet, its Packet body field is an EAP
packet, whose format is illustrated in
Figure 1-4
.
Figure 1-4
The format of an EAP packet
0
15
Code
Data
Length
7
Identifier
2
4
N
In an EAP packet:
z
The Code field indicates the EAP packet type, which can be Request, Response, Success, or
Failure.
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 packet
z
The Type field indicates the EAP authentication type. A value of 1 indicates Identity and that the
packet is used to query the identity of the peer. A value of 4 represents MD5-Challenge (similar to
PPP CHAP) and indicates that the packet includes query information.
z
The Type Date field differs with types of Request and Response packets.
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 Operation Manual
for
information about the format of a RADIUS protocol packet.)
The EAP-message field, whose format is shown in
Figure 1-6
, 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
