• The IEEE 802.1X Port-Based Authentication feature is available only on a switch port.
• If the VLAN to which an IEEE 802.1X port is assigned is shut down, disabled, or removed, the port becomes unauthorized. For example, the port is unauthorized after the access VLAN to which a port is assigned shuts down or is removed.
• When IEEE 802.1X authentication is enabled, ports are authenticated before any other Layer 2 or Layer 3 features are enabled.
• Changes to a VLAN to which an IEEE 802.1X-enabled port is assigned are transparent and do not affect the switch port. For example, a change occurs if a port is assigned to a RADIUS server-assigned VLAN and is then assigned to a different VLAN after reauthentication.
• When IEEE 802.1X authentication is enabled on a port, you cannot configure a port VLAN that is equal to a voice VLAN.
• This feature does not support standard ACLs on the switch port.

• The IEEE 802.1X protocol is supported only on Layer 2 static-access ports, Layer 2 static-trunk ports, voice VLAN-enabled ports, and Layer 3 routed ports.

  Note

  Ethernet interfaces can be configured either as access ports or as trunk ports with the following specifications: An access port can have only one VLAN configured on the interface; it can carry traffic for only one VLAN. A trunk port can have two or more VLANs configured on the interface; it can carry traffic for several VLANs simultaneously.

• The IEEE 802.1X protocol is not supported on the following port types:
  • Dynamic-access ports—If you try to enable IEEE 802.1X authentication on a dynamic-access (VLAN Query Protocol [VQP]) port, an error message appears, and IEEE 802.1X authentication is not enabled. If you try to change an IEEE 802.1X-enabled port to dynamic VLAN assignment, an error message appears, and the VLAN configuration is not changed.
  • Dynamic ports—If you try to enable IEEE 802.1X authentication on a dynamic port, an error message appears, and IEEE 802.1X authentication is not enabled. If you try to change the mode of an IEEE 802.1X-enabled port to dynamic, an error message appears, and the port mode is not changed.
  • Switched Port Analyzer (SPAN) and Remote SPAN (RSPAN) destination ports—You can enable IEEE 802.1X authentication on a port that is a SPAN or RSPAN destination port. However, IEEE 802.1X authentication is disabled until the port is removed as a SPAN or RSPAN destination port. You can enable IEEE 802.1X authentication on a SPAN or RSPAN source port.

  Note	A port in dynamic mode can negotiate with its neighbor to become a trunk port.

• Configuring the same VLAN ID for both access and voice traffic (using the switchport access vlan vlan-id and the switchport voice vlan vlan-id commands) fails if authentication has already been configured on the port.

• Configuring authentication on a port on which you have already configured switchport access vlan vlan-id and switchport voice vlan vlan-id fails if the access VLAN and voice VLAN have been configured with the same VLAN ID.

• 802.1x supplicant is not supported on WAN ports. The feature support is available only for switchports. Use the dot1x pae supplicant command to enable the feature.

In Cisco IOS Release 12.4(11)T, the implementation for IEEE 802.1X authentication changed from the previous releases. When IEEE 802.1X authentication is enabled, information about Port Fast is no longer added to the configuration.

Note	To ensure that information about any IEEE 802.1x-related commands that is entered on a port is automaticallly added to the running configuration to address any backward compatibility issues, use the dot1x pae authenticator command.

With IEEE 802.1X authentication, the devices in the network have specific roles as shown in the figure below.

Figure 1. IEEE 802.1X Device Roles

• Supplicant—Device (workstation) that requests access to the LAN and switch services and responds to requests from the router. The workstation must be running IEEE 802.1X-compliant client software such as that offered in the Microsoft Windows XP operating system. (The supplicant is sometimes called the client.)

  Note	To resolve Windows XP network connectivity and IEEE 802.1X authentication issues, read the Microsoft Knowledge Base article at this URL: http:/​/​support.microsoft.com/​kb/​q303597/​.

• Authentication server—Device that performs the actual authentication of the supplicant. The authentication server validates the identity of the supplicant and notifies the router whether or not the supplicant is authorized to access the LAN and switch services. The Network Access Device (or ISR router in this instance) transparently passes the authentication messages between the supplicant and the authentication server, and the authentication process is carried out between the supplicant and the authentication server. The particular EAP method used will be decided between the supplicant and the authentication server (RADIUS server). The RADIUS security system with EAP extensions is available in Cisco Secure Access Control Server Version 3.0 or later. RADIUS operates in a client and server model in which secure authentication information is exchanged between the RADIUS server and one or more RADIUS clients.

• Authenticator (integrated services router (ISR) or wireless access point)—Router that controls the physical access to the network based on the authentication status of the supplicant. The router acts as an intermediary between the supplicant and the authentication server, requesting identity information from the supplicant, verifying that information with the authentication server, and relaying a response to the supplicant. The router includes the RADIUS client, which is responsible for encapsulating and decapsulating the EAP frames and interacting with the authentication server.

When the authenticator receives EAPOL frames and relays them to the authentication server, the EAPOL is stripped and the remaining EAP frame is reencapsulated in the RADIUS format. The EAP frames are not modified during encapsulation, and the authentication server must support EAP within the native frame format. When the authenticator 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.

During IEEE 802.1X authentication, the router or the supplicant can initiate authentication. If you enable authentication on a port by using the authentication port-control auto interface configuration command, the router initiates authentication when the link state changes from down to up or periodically if the port remains up and unauthenticated. The router sends an EAP-request/identity frame to the supplicant to request its identity. Upon receipt of the frame, the supplicant responds with an EAP-response/identity frame.

Note	Effective with Cisco IOS Release 12.2(33)SXI, the authentication port-control command replaces the dot1xport-control command.

However, if during bootup the supplicant does not receive an EAP-request/identity frame from the router, the supplicant can initiate authentication by sending an EAPOL-start frame, which prompts the router to request the supplicant’s identity.

Note

If IEEE 802.1X authentication is not enabled or supported on the network access device, any EAPOL frames from the supplicant are dropped. If the supplicant does not receive an EAP-request/identity frame after three attempts to start authentication, the supplicant sends frames as if the port is in the authorized state. A port in the authorized state effectively means that the supplicant has been successfully authenticated. For more information, see the Ports in Authorized and Unauthorized States module.

When the supplicant supplies its identity, the router begins its role as the intermediary, passing EAP frames between the supplicant and the authentication server until authentication succeeds or fails. If the authentication succeeds, the router port becomes authorized. If the authentication fails, authentication can be retried, the port might be assigned to a VLAN that provides limited services, or network access is not granted. For more information, see the Ports in Authorized and Unauthorized States module.

The specific exchange of EAP frames depends on the authentication method being used. The figure below shows a message exchange initiated by the supplicant using the One-Time-Password (OTP) authentication method with a RADIUS server.

Figure 2. Message Exchange

To configure IEEE 802.1X port-based authentication, you must enable authentication, authorization, and accounting (AAA) and specify the authentication method list. A method list describes the sequence and authentication method to be queried to authenticate a user.

The AAA process begins with authentication. When IEEE 802.1X port-based authentication is enabled and the device attempting to authenticate is IEEE 802.1x-capable (meaning it supports the supplicant functionality), this event occurs:

• If the supplicant identity is valid and the IEEE 802.1X authentication succeeds, the router grants the supplicant access to the network.

The router reauthenticates a supplicant when this situation occurs:

• Periodic reauthentication is enabled, and the reauthentication timer expires.

You can configure the reauthentication timer to use a router-specific value or to be based on values from the RADIUS server.

After IEEE 802.1X authentication using a RADIUS server is configured, the router uses timers based on the Session-Timeout RADIUS attribute (Attribute [27]) and the Termination-Action RADIUS attribute (Attribute [29]).

The Session-Timeout RADIUS attribute (Attribute [27]) specifies the time after which reauthentication occurs.

The Termination-Action RADIUS attribute (Attribute [29]) specifies the action to take during reauthentication. The actions can be Initialize or ReAuthenticate. When the Initialize action is set (the attribute value is DEFAULT ), the IEEE 802.1x session ends, and connectivity is lost during reauthentication. When the ReAuthenticate action is set (the attribute value is RADIUS-Request), the session is not affected during reauthentication.

You manually reauthenticate the supplicant by entering the dot1x re-authenticate interface interface-name interface-number privileged EXEC command.

You can configure an IEEE 802.1X port for single-host or for multihost mode. In single-host mode (see the figure IEEE 802.1X Device Roles in the Device Roles section of this module), only one supplicant can be authenticated by the IEEE 802.1X-enabled switch port. The router detects the supplicant by sending an EAPOL frame when the port link state changes to the up state. If a supplicant leaves or is replaced with another supplicant, the router changes the port link state to down, and the port returns to the unauthorized state.

In multihost mode, you can attach multiple hosts to a single IEEE 802.1X-enabled port. In this mode, only one of the attached supplicants must be authorized for all supplicants to be granted network access. If the port becomes unauthorized (reauthentication fails or an EAPOL-logoff message is received), the router denies network access to all of the attached supplicants.

Note	Cisco 870 series platforms do not support single-host mode.

During IEEE 802.1X authentication, depending on the port state, the router can grant a supplicant 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 traffic except for IEEE 802.1X authentication, Cisco Discovery Protocol (CDP), and STP packets. When a supplicant is successfully authenticated, the port changes to the authorized state, allowing all traffic for the supplicant to flow normally. If the port is configured as a voice VLAN port, the port allows VoIP traffic and IEEE 802.1X protocol packets before the supplicant is successfully authenticated.

If a client that does not support IEEE 802.1X authentication connects to an unauthorized IEEE 802.1X port, then the router requests the client’s identity. In this situation, if the client does not respond 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 supplicant connects to a port that is not running the IEEE 802.1X standard, the supplicant initiates the authentication process by sending the EAPOL-start frame. When no response is received, the supplicant sends the request for a fixed number of times. Because no response is received, the supplicant begins sending frames as if the port is in the authorized state.

If the supplicant is successfully authenticated (receives an Accept frame from the authentication server), the port state changes to authorized, and all frames from the authenticated supplicant 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 router 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 supplicant logs off, it sends an EAPOL-logoff message, causing the router 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.

Use the IEEE 802.1X—Conditional Logging feature for troubleshooting. When the Conditional Logging feature is enabled, the router generates debugging messages for packets entering or leaving the router on a specified interface; the router will not generate debugging output for packets entering or leaving through a different interface. You can specify the interfaces explicitly. For example, you may want to see only debugging messages for one interface or subinterface. You can also turn on debugging for all interfaces that meet the configured condition. This feature is useful on dial access servers, which have a large number of ports.

Normally, the router will generate debugging messages for every interface, resulting in a large number of messages. The large number of messages consumes system resources, and can affect your ability to find the specific information you need. By limiting the number of debugging messages, you can receive messages related to only the ports you want to troubleshoot.

For more information on conditional logging and enabling conditionally triggered debugging, see the “Enabling Conditionally Triggered Debugging” section of the “Troubleshooting and Fault Management” chapter in the Basic System Management Configuration Guide.

Cisco IOS Release 12.4(11)T provides support for the following MIBs that provide SNMP access to IEEE 802.1X feature components:

• IEEE8021-PAE-MIB

• Cisco-PAE-MIB

The IEEE8021-PAE-MIB supports reporting of the following information:

• The state of the IEEE 802.1X state machine on a particular port

• Statistics associated with the state of the IEEE 802.1X state machine

The Cisco-PAE-MIB provides SNMP support for the logging and reporting of events, including:

• Port mode

• Guest VLAN number (details the Guest VLAN number configured on a port)

• InGuestVLAN (indicates whether a port is in the Guest VLAN)

1.    enable


2.    configure terminal


3.    aaa new-model


4.    aaa authentication dot1x {default | listname} method1 [method2...]


5.    dot1x system-auth-control


6.    identity profile default


7.    interface type slot/port


8.    access-session port-control {auto | force-authorized | force-unauthorized}


9.    dot1x pae [supplicant | authenticator | both]


10.    end


11.    show dot1x

Device> enable

Device# configure terminal

Device(config)# aaa new-model

Device(config)# aaa authentication dot1x default group radius

Device(config)# dot1x system-auth-control

Device(config)# identity profile default

Device(config-identity-prof)# interface fastethernet 0/1

Device(config-if)# access-session port-control auto

Device(config-if)# dot1x pae authenticator

Device(config-if)# end

Device# show dot1x

Note	This section describes IEEE 802.1X security features available only on the switch ports.

1.    enable


2.    configure terminal


3.    radius-server vsa send authentication


4.    interface type number


5.    access-session host-mode {multi-auth | multi-domain | multi-host | single-host} [open]


6.    switchport voice vlan vlan-id


7.    end


8.    show authentication interface type number


9.    copy running-config startup-config

Device> enable

Device# configure terminal

Device(config)# radius-server vsa send authentication

Device(config)# interface fastethernet 2/1

Device(config-if)# access-session host-mode single-host fastethernet 2/1

Device(config-if)# switchport voice vlan 2

Device(config-if)# end

Device# show authentication interface

Device# copy running-config startup-config

1.    enable


2.    configure terminal

Device> enable

Device# configure terminal