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Cisco Catalyst Blade Switch 3130 for Dell Software Configuration Guide
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Chapter9 Configuring IEEE 802 . 1x Port-Based Authentication Understanding IEEE 802.1x Port-Based Authentication
Ports in Authorized and Unauthorized States
During IEEE 802.1x authentication, depending on the switch port state, the switch can grant a client
access to the network. The port starts in the unauthorized state. While in this state, the port that is not
configured as a voice VLAN port disallows all ingress and egress traffic except for IEEE 802.1x
authentication, CDP, and STP packets. When a client is successfully authenticated, the port changes to
the authorized state, allowing all traffic for the cli ent to flo w normally. If the port is configured as a voice
VLAN port, the port allows VoIP traffic and IEEE 802.1x protocol packets before the client is
successfully authenticated.
If a client that does not support IEEE 802.1x authentication connects to an unauthorized IEEE 802 .1x
port, the switch requests the client’s identity. In this situation, the client does not res pond to the request,
the port remains in the unauthorized state, and the client is not granted access to the network.
In contrast, when an IEEE 802.1x-enabled client connects to a port that is not running the IEEE 802.1x
standard, the client initiates the authentication process by sending the EAPOL-start frame. When no
response is received, the client sends the request for a fixed number of times. Because no response is
received, the client begins sending frames as if the port is in the authorized state.
You control the port authorization state by using the dot1x port-control interface configuration
command and these keywords:
•force-authorized—disables IEEE 802.1x authentication and causes the port to change to the
authorized state without any authentication exchange required. The port sends a nd r eceives normal
traffic without IEEE 802.1x-based authentication of the client. This is the default setting.
•force-unauthorized—causes the port to remain in the unauthorized state, ignoring all attempts by
the client to authenticate. The switch cannot provide authentication services to the cl ient through the
port.
•auto—enables IEEE 802.1x authentication and causes the p ort to b egin i n the un auth oriz ed sta te,
allowing only EAPOL frames to be sent and received through the port. The authentication process
begins when the link state of the port changes from down to up or when an EAPOL-start frame is
received. The switch requests the identity of the client and begins relaying authentication messages
between the client and the authentication server. Each client attempting to access the network is
uniquely identified by the switch by using the client MAC address.
If the client is successfully authenticated (receives an Accept frame fro m the au th en tic atio n server), the
port state changes to authorized, and all frames from the authenticated client are allowed through the
port. If the authentication fails, the port remains in the unauthorized state, but authentication can be
retried. If the authentication server cannot be reached, the switch can resend the request. If no response
is received from the server after the specified number of attempts, authentication fails, and network
access is not granted.
When a client logs off, it sends an EAPOL-logoff message, causing the switch port to change to the
unauthorized state.
If the link state of a port changes from up to down, or if an EAPOL-logoff frame is received, the port
returns to the unauthorized state.
IEEE 802.1x Authentication and Switch Stacks
If a switch is added to or removed from a switch stack, IEEE 802.1x authentication is not affected as
long as the IP connectivity between the RADIUS server and the stack remains intact. This statem ent also
applies if the stack master is removed from the switch stack. Note that if the stack master fails, a stack
member becomes the new stack master by using the election process described in Chapter 5, “Managing
Switch Stacks,” and the IEEE 802.1x authentication process continues as usual.