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User’s Manual of SGSD-1022 / SGSD-1022P
SGSW-2840 / SGSW-2840P
281
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 2-43” shows a message
exchange initiated by the client using the One-Time-Password (OTP) authentication method with a RADIUS server.