Figure 172 EAP Frame Format

Ethernet Header

802,tx Header

EAP Payload

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Code

5D

Length

Data

1 Byte

1 Byte

2 Bytes

0+ Bytes

The field descriptions are as follows:

• Code The Code field is 1 octet and identifies the type of EAP packet. Table 17-2 shows the assigned EAP Codes.

Table 17-2. Assigned EAP Codes

Code

Description

1

Request

2

Response

3

Success

4

Failure

EAP only defines codes 1 through 4. Any EAP packets with other codes are silently discarded.

• Identifier The Identifier field is 1 octet and aids in matching Responses with Requests.

• Length The Length field is 2 octets and indicates the length, in octets, of the EAP packet including the Code, Identifier, Length, and Data fields. Octets outside the range of the Length field should be treated as data link layer padding and will be ignored upon reception. A message with the Length field set to a value larger than the number of received octets will be silently discarded.

• Data The Data field is 0 or more octets. The Code field determines the format of the Data field.

On LAN media, the supplicant and the authenticator communicate using an encapsulation technique known as EAP over LANs (EAPOL). EAPOL supports various media types, such as Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), and WLANs. EAPOL is encapsulated EAP messages that can be handled directly by a LAN MAC service. Figure 17-3 shows the EAPOL frame format.

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