3Com E4500-24 Cli Configuration Manual page 324

Figure 1-8 802.1x authentication procedure (in EAP relay mode)
EAPOL
Supplicant system
PAE
EAPOL - Start
EAP- Request / Identity
EAP- Response / Identity
EAP- Request / MD5 challenge
EAP- Response / MD5 challenge
EAP-Success
Handshake request
[ EAP- Request / Identity ]
Handshake response
[ EAP- Response / Identity ]
EAPOL -Logoff
The detailed procedure is as follows:
A supplicant system launches an 802.1x client to initiate an access request by sending an
EAPoL-start packet to the switch, with its user name and password provided. The 802.1x client
program then forwards the packet to the switch to start the authentication process.
Upon receiving the authentication request packet, the switch sends an EAP-request/identity packet
to ask the 802.1x client for the user name.
The 802.1x client responds by sending an EAP-response/identity packet to the switch with the user
name contained in it. The switch then encapsulates the packet in a RADIUS Access-Request
packet and forwards it to the RADIUS server.
Upon receiving the packet from the switch, the RADIUS server retrieves the user name from the
packet, finds the corresponding password by matching the user name in its database, encrypts the
password using a randomly-generated key, and sends the key to the switch through an RADIUS
access-challenge packet. The switch then sends the key to the 802.1x client.
Upon receiving the key (encapsulated in an EAP-request/MD5 challenge packet) from the switch,
the client program encrypts the password of the supplicant system with the key and sends the
encrypted password (contained in an EAP-response/MD5 challenge packet) to the RADIUS server
through the switch. (Normally, the encryption is irreversible.)
The RADIUS server compares the received encrypted password (contained in a RADIUS
access-request packet) with the locally-encrypted password. If the two match, it will then send
Authenticator system
PAE
(EAP- Response / Identity)
( EAP- Request / MD5 challenge)
( EAP- Response / MD5 challenge)
Port authorized
......
Port unauthorized
1-7
EAPOR
RADUIS
RADIUS Access - Request
RADIUS Access -Challenge
RADIUS Access - Request
RADIUS Access -Accept
(EAP-Success)
Handshake timer
server