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Client—the device (workstation) that requests access to the LAN and switch services and responds to requests
from the switch. The workstation must be running 802.1X-compliant client software such as that offered in the
Microsoft Windows XP operating system. (The client is the supplicant in the IEEE 802.1X specification.)
Authentication server—performs the actual authentication of the client. The authentication server validates the
identity of the client and notifies the switch whether or not the client is authorized to access the LAN and switch
services. Because the switch acts as the proxy, the authentication service is transparent to the client. In this
release, the Remote Authentication Dial-In User Service (RADIUS) security system with Extensible
Authentication Protocol (EAP) extensions is the only supported authentication server; it is available in Cisco
Secure Access Control Server version 3.0. RADIUS operates in a client/server model in which secure
authentication information is exchanged between the RADIUS server and one or more RADIUS clients.
Switch (802.1X device)—controls the physical access to the network based on the authentication status of the
client. The switch acts as an intermediary (proxy) between the client and the authentication server, requesting
identity information from the client, verifying that information with the authentication server, and relaying a
response to the client. The switch includes the RADIUS client, which is responsible for encapsulating and
decapsulating the Extensible Authentication Protocol (EAP) frames and interacting with the authentication server.
When the switch receives EAPOL frames and relays them to the authentication server, the Ethernet header is
stripped and the remaining EAP frame is re-encapsulated in the RADIUS format. The EAP frames are not
modified or examined during encapsulation, and the authentication server must support EAP within the native
frame format. When the switch receives frames from the authentication server, the server's frame header is
removed, leaving the EAP frame, which is then encapsulated for Ethernet and sent to the client.
Authentication Initiation and Message Exchange
The switch or the client can initiate authentication. If you enable authentication on a port by using the dot1x port-control
auto interface configuration command, the switch must initiate authentication when it determines that the port link state
transitions from down to up. It then sends an EAP-request/identity frame to the client to request its identity (typically, the
switch sends an initial identity/request frame followed by one or more requests for authentication information). Upon
receipt of the frame, the client responds with an EAP-response/identity frame.
However, if during bootup, the client does not receive an EAP-request/identity frame from the switch, the client can initiate
authentication by sending an EAPOL-start frame, which prompts the switch to request the client's identity
If 802.1X is not enabled or supported on the network access device, any EAPOL frames from the
client are dropped. If the client does not receive an EAP-request/identity frame after three attempts
to start authentication, the client transmits frames as if the port is in the authorized state. A port in
the authorized state effectively means that the client has been successfully authenticated.
When the client supplies its identity, the switch begins its role as the intermediary, passing EAP frames between the client
User's Manual of ISW-1022M
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