z
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.
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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
NOTICE:
If 802.1X is not enabled or supported on the network access device, any EAPOL frames from the client are
