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Cisco IOS software supports the RADIUS CoA extensions defined in RFC 5176 that are typically used in a push model to allow the dynamic reconfiguring of sessions from external AAA or policy servers. Per-session CoA requests are supported for session identification, session termination, host reauthentication, port shutdown, and port bounce. This model comprises one request (CoA-Request) and two possible response codes:

• CoA acknowledgement (ACK) [CoA-ACK]

• CoA nonacknowledgement (NAK) [CoA-NAK]

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

The table below shows the RADIUS CoA commands and vendor-specific attributes (VSAs) supported by Identity-Based Networking Services. All CoA commands must include the session identifier between the device and the CoA client.

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 VSA)

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

• IPv6 Attributes, which can be one of the following:

  • Framed-IPv6-Prefix (IETF attribute #97) and Framed-Interface-Id (IETF attribute #96), which together create a full IPv6 address per RFC 3162
  • Framed-IPv6-Address

• Plain IP Address (IETF attribute #8)

If more than one session identification attribute is included in the message, all of the attributes must match the session or the device returns a Disconnect-NAK or CoA-NAK with the error code “Invalid Attribute Value.”

For CoA requests targeted at a particular enforcement policy, the device returns a CoA-NAK with the error code “Invalid Attribute Value” if any of the above session identification attributes are included in the message.

The CoA activate service command can be used to activate a service template on a session. The AAA server sends the request in a standard CoA-Request message using the following VSAs:

Cisco:Avpair=“subscriber:command=activate-service”

Cisco:Avpair=“subscriber:service-name=<service-name>”

Cisco:Avpair=“subscriber:precedence=<precedence-number>”

Cisco:Avpair=“subscriber:activation-mode=replace-all”

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 a session, it returns a CoA-NAK message with the “Session Context Not Found” error-code attribute. If the device locates a session, it initiates an activate template operation for the hosting port and a CoA-ACK is returned. If activating the template fails, a CoA-NAK message is returned with the Error-Code attribute set to the appropriate 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.

The CoA deactivate service command can be used to deactivate a service template on a session. The AAA server sends the request in a standard CoA-Request message using the following VSAs:

Cisco:Avpair=“subscriber:command=deactivate-service”

Cisco:Avpair=“subscriber:service-name=<service-name>”

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 a session, it returns a CoA-NAK message with the “Session Context Not Found” error-code attribute. If the device locates a session, it initiates a deactivate template operation for the hosting port and a CoA-ACK is returned. If deactivating the template fails, a CoA-NAK message is returned with the Error-Code attribute set to the appropriate 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.

The CoA bounce host port command terminates a session and bounces the port (initiates a link down event followed by a link up event). The AAA server sends the request in a standard CoA-Request message with 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” section. 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 ten seconds, reenables it (port bounce), and returns a CoA-ACK.

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.

The CoA bounce port command is useful as a last resort when an endpoint needs to acquire a new IP address after a change in authorization and this is the only way to indicate to the endpoint to restart the DHCP process. This 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. This command can cause a link flap on an authentication port, which triggers DHCP renegotiation from one or more hosts connected to this port.

The CoA disable host port command administratively shuts down the authentication port that is hosting a session, which terminates the session. The AAA server sends the request in a standard CoA-Request message with 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.

The CoA session query command requests service information about a subscriber session. The AAA server sends the request in a standard CoA-Request message containing the following VSA:

Cisco:Avpair=“subscriber:command=session-query”

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 a session, it returns a CoA-NAK message with the “Session Context Not Found” error-code attribute. If the device locates a session, it performs a session query operation on the session 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 initiate session authentication, the AAA server sends a standard CoA-Request message containing the following VSAs:

Cisco:Avpair=“subscriber:command=reauthenticate”

Cisco:Avpair=“subscriber:reauthenticate-type=<last | rerun>”

“reauthenticate-type” defines whether the CoA reauthentication request uses the authentication method that last succeeded on the session or whether the authentication process is completely rerun.

The following rules apply:

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 resent 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.

A CoA Disconnect-Request command terminates a session without disabling the host port. This command 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.

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.

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. When you want to restore network access on the port, reenable it using a non-RADIUS mechanism.