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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 and
the authentication server until authentication succeeds or fails. If the authentication succeeds, the switch port becomes
authorized.
The specific exchange of EAP frames depends on the authentication method being used.
exchange initiated by the client using the One-Time-Password (OTP) authentication method with a RADIUS server.
User's Manual of GS-4210 Series
285
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