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Software Configuration Guide—Release 12.2(25)SG
OL-7659-03
Chapter29 Understanding and Conf iguring 802.1X Port-Based Authentication
Understanding 802.1X Port-Based Authentication
support EAP within the native frame format. When the switch receives frames from the
authentication server, the frame header is removed from the server, leaving the EAP frame, whi ch
is then encapsulated for Ethernet and sent to the client.
Cisco devices that are capable of functioning as an 802.1X network access point include
Catalyst 4500 series switches, the Catalyst3550 multilayer switch, the Catalyst 2950 switch, and a
Cisco Airnet series wireless access point. These devices must be running software that supports the
RADIUS client and 802.1X.
•Authentication server—Performs the actual authentication of the client. The authentication server
validates the identity of the client and notifies the switch that the client is authorized to access the
LAN and switch services. (The only supported authentication server is the RADIUS authentication
server with EAP extensions; it is available in Cisco Secure Access Control Server version 3.2 and
later.)
802.1x and Network Access Control
Network Access Control is a feature that allows port access policies to be influenced by the anti-virus
posture of the authenticating device.
Anti-virus posture includes such elements as the operating system running on the device, the opera ting
system version, whether anti-virus software is installed, what version of anti-virus signatures is
available, etc. If the authenticating device has a NAC-aware 802.1X supplicant and the authentication
server is configured to support NAC via 802.1X, anti-virus posture information will be automatically
included as part of the 802.1X authentication exchange.
For information on configuring NAC, refer to the URL:
http://www.cisco.com/en/US/products/hw/switches/ps4324/prod_configuration_guide09186a00805764
fd.html
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 has changed. 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 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 authent ication method being used. Figure 29-2
shows a message exchange that is initiated by the client using the One-Time Password (OTP)
authentication method with an authentication server.