Interlogix NS3500-28T-4S User Manual - Manual (Page 223)

223
 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.