∙Packet body: Content of the packet. When the EAPOL packet type is EAP-Packet, the Packet body field contains an EAP packet.

EAP over RADIUS

RADIUS adds two attributes, EAP-Message and Message-Authenticator, for supporting EAP authentication. For the RADIUS packet format, see the chapter “RADIUS configuration.”

EAP-Message

RADIUS encapsulates EAP packets in the EAP-Message attribute, as shown in a. The Type field takes 79, and the Value field can be up to 253 bytes. If an EAP packet is longer than 253 bytes, RADIUS encapsulates it in multiple EAP-Message attributes.

a.EAP-Message attribute format

0

7

15

N

 

 

 

 

 

Type

Length

String

 

 

 

 

EAP packets

Message-Authenticator

RADIUS includes the Message-Authenticator attribute in all packets that have an EAP-Message attribute to check their integrity. The packet receiver drops the packet if the calculated packet integrity checksum is different than the Message-Authenticator attribute value. The Message-Authenticator prevents EAP authentication packets from being tampered with during EAP authentication.

a.Message-Authenticator attribute format

Initiating 802.1X authentication

Both the 802.1X client and the access device can initiate 802.1X authentication.

802.1X client as the initiator

The client sends an EAPOL-Start packet to the access device to initiate 802.1X authentication. The destination MAC address of the packet is the IEEE 802.1X specified multicast address 01-80-C2-00-00-03 or the broadcast MAC address. If any intermediate device between the client and the authentication server does not support the multicast address, you must use an 802.1X client, the iNode 802.1X client for example, that can send broadcast EAPOL-Start packets.

Access device as the initiator

The access device initiates authentication, if a client, the 802.1X client available with Windows XP for example, cannot send EAPOL-Start packets.

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