PLANET VC-2400MR48 - Manual (Page 126)

User’s Manual of VC-820M / VC-2400MR Series
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.
z 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. “ Figure 4-14-2 ” shows a message
exchange initiated by the client using the One-Time-Password (OTP) authentication method with a RADIUS server.
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