EAP relay
Figure 31 shows the basic 802.1X authentication procedure in EAP relay mode, assuming that EAP-MD5 is used.
Figure 31: 802.1X authentication procedure in EAP relay mode
When a user launches the 802.1X client software and enters a registered username and password, the 802.1X client software sends an EAPOL-Start packet to the network access device.
The network access device responds with an Identity EAP-Request packet to ask for the client username.
In response to the Identity EAP-Request packet, the client sends the username in an Identity EAP-Response packet to the network access device.
The network access device relays the Identity EAP-Response packet in a RADIUS Access-Request packet to the authentication server.
The authentication server uses the identity information in the RADIUS Access-Request to search its user database. If a matching entry is found, the server uses a randomly generated challenge (EAP-Request/MD5 challenge) to encrypt the password in the entry, and sends the challenge in a RADIUS Access-Challenge packet to the network access device.
The network access device relays the EAP-Request/MD5 Challenge packet in a RADIUS Access-Request packet to the client.
The client uses the received challenge to encrypt the password, and sends the encrypted password in an EAP-Response/MD5 Challenge packet to the network access device.
The network access device relays the EAP-Response/MD5 Challenge packet in a RADIUS Access-Request packet to the authentication server.
The authentication server compares the received encrypted password with the one it generated at step 5. If the two are identical, the authentication server considers the client valid and sends a RADIUS Access-Accept packet to the network access device.
Upon receiving the RADIUS Access-Accept packet, the network access device sends an EAP-Success packet to the client, and sets the controlled port in the authorized state so the client can access the network.
After the client comes online, the network access device periodically sends handshake requests to check whether the client is still online. By default, if two consecutive handshake attempts fail, the device logs off the client.
Upon receiving a handshake request, the client returns a response. If the client fails to return a response after a certain number of consecutive handshake attempts (two by default), the network access device logs off the client. This handshake mechanism enables timely release of the network resources used by 802.1X users that have abnormally gone offline.
The client can also send an EAPOL-Logoff packet to ask the network access device for a logoff. Then
In response to the EAPOL-Logoff packet, the network access device changes the status of the controlled port from authorized to unauthorized and sends an EAP-Failure packet to the client.