RADIUS Change of Authorization

The RADIUS Change of Authorization (CoA) feature provides a mechanism to change the attributes of an authentication, authorization, and accounting (AAA) session after it is authenticated. When a policy changes for a user or user group in AAA, administrators can send the RADIUS CoA packets from the AAA server such as a Cisco Secure Access Control Server (ACS) to reinitialize authentication and apply the new policy.

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Information About RADIUS Change of Authorization

About RADIUS Change of Authorization

A standard RADIUS interface is typically used in a pulled model, in which the request originates from a device attached to a network and the response is sent from the queried servers. The Cisco software supports the RADIUS CoA request defined in RFC 5176 that is used in a pushed model, in which the request originates from the external server to the device attached to the network, and enables the dynamic reconfiguring of sessions from external authentication, authorization, and accounting (AAA) or policy servers.

Use the following per-session CoA requests:

  • Session reauthentication

  • Session termination

  • Session termination with port shutdown

  • Session termination with port bounce

  • Security and Password

  • Accounting

CoA Requests

CoA requests, as described in RFC 5176, are used in a pushed model to allow for session identification, host reauthentication, and session termination. The model comprises one request (CoA-Request) and two possible response codes:

  • CoA acknowledgment (ACK) [CoA-ACK]

  • CoA non-acknowledgment (NAK) [CoA-NAK]

The request is initiated from a CoA client (typically a RADIUS or policy server) and directed to the device that acts as a listener.

RFC 5176 Compliance

The Disconnect Request message, which is also referred to as Packet of Disconnect (POD), is supported by the device for a session termination.

The following table shows the IETF attributes that are supported for the RADIUS Change of Authorization (CoA) feature.

Table 1 Supported IETF Attributes

Attribute Number

Attribute Name

24

State

31

Calling-Station-ID

44

Acct-Session-ID

80

Message-Authenticator

101

Error-Cause

The following table shows the possible values for the Error-Cause attribute.

Table 2 Error-Cause Values

Value

Explanation

201

Residual Session Context Removed

202

Invalid EAP Packet (Ignored)

401

Unsupported Attribute

402

Missing Attribute

403

NAS Identification Mismatch

404

Invalid Request

405

Unsupported Service

406

Unsupported Extension

407

Invalid Attribute Value

501

Administratively Prohibited

502

Request Not Routable (Proxy)

503

Session Context Not Found

504

Session Context Not Removable

505

Other Proxy Processing Error

506

Resources Unavailable

507

Request Initiated

508

Multiple Session Selection Unsupported

CoA Request Response Code

The CoA Request Response code can be used to issue a command to the device. The supported commands are listed in the “CoA Request Commands” section.

The packet format for a CoA Request Response code as defined in RFC 5176 consists of the following fields: Code, Identifier, Length, Authenticator, and Attributes in the Type:Length:Value (TLV) format.

The Attributes field is used to carry Cisco VSAs.

Session Identification

For disconnect and CoA requests targeted at a particular session, the device locates the session based on one or more of the following attributes:

  • Acct-Session-Id (IETF attribute #44)

  • Audit-Session-Id (Cisco vendor-specific attribute (VSA))

  • Calling-Station-Id (IETF attribute #31, which contains the host MAC address)

Unless all session identification attributes included in the CoA message match the session, the device returns a Disconnect-NAK or CoA-NAK with the “Invalid Attribute Value” error-code attribute.


Note

A CoA NAK message is not sent for all CoA requests with a key mismatch. The message is sent only for the first three requests for a client. After that, all the packets from that client are dropped. When there is a key mismatch, the response authenticator sent with the CoA NAK message is calculated from a dummy key value.

CoA ACK Response Code

If an authorization state is changed successfully, a positive acknowledgment (ACK) is sent. The attributes returned within a CoA ACK can vary based on the CoA Request.

CoA NAK Response Code

A negative acknowledgment (NAK) indicates a failure to change the authorization state and can include attributes that indicate the reason for the failure.

CoA Request Commands

The commands supported on the device are shown in the table below. All CoA commands must include the session identifier between the device and the CoA client.

Table 3 CoA Request Commands Supported on the Device

Command

Cisco VSA

Bounce host port

Cisco:Avpair=“subscriber:command=bounce-host-port”

Disable host port

Cisco:Avpair=“subscriber:command=disable-host-port”

Reauthenticate host

Cisco:Avpair=“subscriber:command=reauthenticate”

Terminate session

This is a standard disconnect request that does not require a VSA

Session Reauthentication

To initiate session reauthentication, the authentication, authorization, and accounting (AAA) server sends a standard CoA-Request message that contains a Cisco VSA and one or more session identification attributes. The Cisco VSA is in the form of Cisco:Avpair=“subscriber:command=reauthenticate”.

The current session state determines the device’s response to the message in the following scenarios:

  • If the session is currently authenticated by IEEE 802.1x, the device responds by sending an Extensible Authentication Protocol over LAN (EAPoL)-RequestId message to the server.

  • If the session is currently authenticated by MAC authentication bypass (MAB), the device sends an access request to the server, passing the same identity attributes used for the initial successful authentication.

  • If session authentication is in progress when the device receives the command, the device terminates the process and restarts the authentication sequence, starting with the method configured to be attempted first.

Session Termination

A CoA Disconnect-Request terminates the session without disabling the host port. CoA Disconnect-Request termination causes reinitialization of the authenticator state machine for the specified host, but does not restrict the host’s access to the network. If the session cannot be located, the device returns a Disconnect-NAK message with the “Session Context Not Found” error-code attribute. If the session is located, the device terminates the session. After the session has been completely removed, the device returns a Disconnect-ACK message.

To restrict a host’s access to the network, use a CoA Request with the Cisco:Avpair=“subscriber:command=disable-host-port” VSA. This command is useful when a host is known to cause problems on the network and network access needs to be immediately blocked for the host. If you want to restore network access on the port, reenable it using a non-RADIUS mechanism.

CoA Request Disable Host Port

The RADIUS server CoA disable port command administratively shuts down the authentication port that is hosting a session, resulting in session termination. This command is useful when a host is known to cause problems on the network and network access needs to be immediately blocked for the host. If you want to restore network access on the port, reenable it using a non-RADIUS mechanism. This command is carried in a standard CoA-Request message that has the following VSA:

Cisco:Avpair=“subscriber:command=disable-host-port”

Because this command is session-oriented, it must be accompanied by one or more of the session identification attributes described in the “Session Identification” section. If the device cannot locate the session, it returns a CoA-NAK message with the “Session Context Not Found” error-code attribute. If the device locates the session, it disables the hosting port and returns a CoA-ACK message.

If the device fails before returning a CoA-ACK to the client, the process is repeated on the new active device when the request is re-sent from the client. If the device fails after returning a CoA-ACK message to the client but before the operation is complete, the operation is restarted on the new active device.

To ignore the RADIUS server CoA disable port command, see the “Configuring the Device to Ignore Bounce and Disable RADIUS CoA Requests” section.

CoA Request Bounce Port

A RADIUS server CoA bounce port sent from a RADIUS server can cause a link flap on an authentication port, which triggers DHCP renegotiation from one or more hosts connected to this port. This incident can occur when there is a VLAN change and the endpoint is a device (such as a printer) that does not have a mechanism to detect a change on this authentication port. The CoA bounce port is carried in a standard CoA-Request message that contains the following VSA:

Cisco:Avpair=“subscriber:command=bounce-host-port”

Because this command is session-oriented, it must be accompanied by one or more of the session identification attributes described in the Session Identification. If the session cannot be located, the device returns a CoA-NAK message with the “Session Context Not Found” error-code attribute. If the session is located, the device disables the hosting port for a period of 10 seconds, reenables it (port-bounce), and returns a CoA-ACK.

To ignore the RADIUS server CoA bounce port, see the “Configuring the Device to Ignore Bounce and Disable RADIUS CoA Requests” section.

How to Configure RADIUS Change of Authorization

Configuring RADIUS Change of Authorization

SUMMARY STEPS

    1.    enable

    2.    configure terminal

    3.    aaa new-model

    4.    aaa server radius dynamic-author

    5.    client {ip-address | name [vrf vrf-name]} server-key [0 | 7] string

    6.    port port-number

    7.    auth-type {any | all | session-key}

    8.    ignore session-key

    9.    ignore server-key

    10.    exit


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Device> enable
     

    Enables privileged EXEC mode.

    • Enter your password if prompted.

     
    Step 2 configure terminal


    Example:
    Device# configure terminal
     

    Enters global configuration mode.

     
    Step 3 aaa new-model


    Example:
    Device(config)# aaa new-model
     

    Enables authentication, authorization, and accounting (AAA) globally.

     
    Step 4 aaa server radius dynamic-author


    Example:
    Device(config)# aaa server radius dynamic-author
     

    Enters dynamic authorization local server configuration mode and specifies a RADIUS client from which a device accepts Change of Authorization (CoA) and disconnect requests. Configures the device as a AAA server to facilitate interaction with an external policy server.

     
    Step 5client {ip-address | name [vrf vrf-name]} server-key [0 | 7] string


    Example:
    Device(config-locsvr-da-radius)# client 10.0.0.1
     

    Configures the RADIUS key to be shared between a device and RADIUS clients.

     
    Step 6port port-number


    Example:
    Device(config-locsvr-da-radius)# port 3799
     

    Specifies the port on which a device listens for RADIUS requests from configured RADIUS clients.

    Note   

    The default port for packet of disconnect is 1700. Port 3799 is required to interoperate with ACS 5.1.

     
    Step 7auth-type {any | all | session-key}


    Example:
    Device(config-locsvr-da-radius)# auth-type all
     

    Specifies the type of authorization that the device must use for RADIUS clients. The client must match the configured attributes for authorization.

     
    Step 8ignore session-key


    Example:
    Device(config-locsvr-da-radius)# ignore session-key
     

    (Optional) Configures the device to ignore the session key.

     
    Step 9ignore server-key


    Example:
    Device(config-locsvr-da-radius)# ignore server-key
     

    (Optional) Configures the device to ignore the server key.

     
    Step 10exit


    Example:
    Device(config-locsvr-da-radius)# exit
     

    Returns to global configuration mode.

     

    Configuring a Device to Ignore Bounce and Disable RADIUS CoA Requests

    When an authentication port is authenticated with multiple hosts and there is a Change of Authorization (CoA) request for one host to flap on this port or one host session to be terminated on this port, the other hosts on this port are also affected. Thus, an authenticated port with multiple hosts can trigger a DHCP renegotiation from one or more hosts in the case of a flap, or it can administratively shut down the authentication port that is hosting the session for one or more hosts.

    Perform the following steps to configure the device to ignore RADIUS server Change of Authorization (CoA) requests in the form of a bounce port command or disable port command.

    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    aaa new-model

      4.    authentication command bounce-port ignore

      5.    authentication command disable-port ignore

      6.    end


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Device> enable
       

      Enables privileged EXEC mode.

      • Enter your password if prompted.

       
      Step 2 configure terminal


      Example:
      Device# configure terminal
       

      Enters global configuration mode.

       
      Step 3 aaa new-model


      Example:
      Device(config)# aaa new-model
       

      Enables authentication, authorization, and accounting (AAA) globally.

       
      Step 4 authentication command bounce-port ignore


      Example:
      Device(config)# authentication command bounce-port ignore
       

      (Optional) Configures the device to ignore a RADIUS server bounce port command that causes a host to link flap on an authentication port, which causes DHCP renegotiation from one or more hosts connected to this port.

       
      Step 5 authentication command disable-port ignore


      Example:
      Device(config)# authentication command disable-port ignore
       
      (Optional) Configures the device to ignore a RADIUS server CoA disable port command that administratively shuts down the authentication port that hosts one or more host sessions.

      • The shutting down of the port causes session termination.

       
      Step 6 end


      Example:
      Device(config)# end
       

      Returns to privileged EXEC mode.

       

      Configuring the Dynamic Authorization Service for RADIUS CoA

      Perform the following steps to enable the device as an authentication, authorization, and accounting (AAA) server for the dynamic authorization service. This service supports the Change of Authorization (CoA) functionality that pushes the policy map in an input and output direction.

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    aaa new-model

        4.    aaa server radius dynamic-author

        5.    client {ip-addr | hostname} [server-key [0 | 7] string]

        6.    domain {delimiter character | stripping | [right-to-left]}

        7.    port port-num

        8.    end


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Device> enable
         

        Enables privileged EXEC mode.

        • Enter your password if prompted.

         
        Step 2 configure terminal


        Example:
        Device# configure terminal
         

        Enters global configuration mode.

         
        Step 3 aaa new-model


        Example:
        Device(config)# aaa new-model
         

        Enables AAA globally.

         
        Step 4 aaa server radius dynamic-author


        Example:
        Device(config)# aaa server radius dynamic-author
         

        Sets up the local AAA server for the dynamic authorization service, which must be enabled to support the CoA functionality to push the policy map in an input and output direction, and enters dynamic authorization local server configuration mode.

        • In this mode, the RADIUS application commands are configured.

         
        Step 5 client {ip-addr | hostname} [server-key [0 | 7] string]


        Example:
        Device(config-locsvr-da-radius)# client 192.168.0.5 server-key cisco1
         

        Configures the IP address or hostname of the AAA server client.

        • Use the optional server-key keyword and string argument to configure the server key at the client level.

        Note   

        Configuring the server key at the client level overrides the server key configured at the global level.

         
        Step 6 domain {delimiter character | stripping | [right-to-left]}


        Example:
        Device(config-locsvr-da-radius)# domain stripping right-to-left
         

        (Optional) Configures username domain options for the RADIUS application.

        • The delimiter keyword specifies the domain delimiter. One of the following options can be specified for the character argument: @, /, $, %, \, #, or -.

        • The stripping keyword compares the incoming username with the names oriented to the left of the @ domain delimiter.

        • The right-to-left keyword terminates the string at the first delimiter going from right to left.

         
        Step 7 port port-num


        Example:
        Device(config-locsvr-da-radius)# port 3799
         

        Configures the UDP port for CoA requests.

         
        Step 8 end


        Example:
        Device(config-locsvr-da-radius)# end
         

        Returns to privileged EXEC mode.

         

        Monitoring and Troubleshooting RADIUS Change of Authorization

        The following commands can be used to monitor and troubleshoot the RADIUS Change of Authorization feature:

        Table 4 Monitoring and Troubleshooting RADIUS Change of Authorization

        Command

        Purpose

        debug aaa coa

        Displays debug information for CoA processing.

        debug aaa pod

        Displays debug messages related to packet of disconnect (POD) packets.

        debug radius

        Displays information associated with RADIUS.

        show aaa attributes protocol radius

        Displays the mapping between an authentication, authorization, and accounting (AAA) attribute number and the corresponding AAA attribute name.

        Configuration Examples for RADIUS Change of Authorization

        Example: Configuring RADIUS Change of Authorization

        Device> enable
Device# configure terminal
Device(config)# aaa new-model
Device(config)# aaa server radius dynamic-author
Device(config-locsvr-da-radius)# client 10.0.0.1 
Device(config-locsvr-da-radius)# server-key cisco123
Device(config-locsvr-da-radius)# port 3799 
Device(config-locsvr-da-radius)# auth-type all
Device(config-locsvr-da-radius)# ignore session-key
Device(config-locsvr-da-radius)# ignore server-key
Device(config-locsvr-da-radius)# end

        Example: Configuring a Device to Ignore Bounce and Disable a RADIUS Requests

        Device> enable
Device# configure terminal
Device(config)# aaa new-model
Device(config)# authentication command bounce-port ignore
Device(config)# authentication command disable-port ignore
Device(config)# end

        Example: Configuring the Dynamic Authorization Service for RADIUS CoA

        The following example shows how to configure the device as a authentication, authorization, and accounting (AAA) server to support Change of Authorization (CoA) functionality that pushes the policy map in an input and output direction: 

        Device> enable
Device# configure terminal
Device(config)# aaa new-model
Device(config)# aaa server radius dynamic-author
Device(config-locsvr-da-radius)# client 192.168.0.5 server-key cisco1
Device(config-locsvr-da-radius)# domain delimiter @
Device(config-locsvr-da-radius)# port 3799
Device(config-locsvr-da-radius)# end

        Additional References for RADIUS Change of Authorization

        Related Documents

        Related Topic

        Document Title

        Cisco IOS commands

        Cisco IOS Master Command List, All Releases

        Security commands

        Configuring AAA

        Authentication, Authorization, and Accounting Configuration Guide

        Standards and RFCs

        Standard/RFC

        Title

        RFC 2903

        Generic AAA Architecture

        RFC 5176

        Dynamic Authorization Extensions to Remote Authentication Dial In User Service(RADIUS)

        Technical Assistance

        Description

        Link

        The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. Access to most tools on the Cisco Support and Documentation website requires a Cisco.com user ID and password.

        http:/​/​www.cisco.com/​cisco/​web/​support/​index.html

        Feature Information for RADIUS Change of Authorization

        The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

        Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.
        Table 5 Feature Information for RADIUS Change of Authorization

        Feature Name

        Releases

        Feature Information

        RADIUS Change of Authorization

        Cisco IOS XE 2.1

        The RADIUS Change of Authorization (CoA) feature provides a mechanism to change the attributes of an AAA session after it is authenticated. When policy changes for a user or user group in AAA, administrators can send the RADIUS CoA packets from the AAA server, such as the Cisco Secure Access Control Server (ACS), to reinitialize authentication and apply the new policy.

        The following commands were introduced or modified: aaa server radius dynamic-author, authentication command bounce-port ignore, and authentication command disable-port ignore.