Administrator Guide

Support for Change of Authorization and Disconnect
Messages packets
The Network Access Server (NAS) uses RADIUS to authenticate AAA or dot1x user-access to the switch. The RADIUS service does not
support unsolicited messages sent from the RADIUS server to the NAS.
However, there are many instances in which it is desirable for changes to be made to session characteristics, without requiring the NAS to
initiate the exchange. For example, it may be desirable for administrators to be able to terminate user sessions in progress.
Alternatively, if the user changes authorization level, this change may require that authorization attributes be added or deleted from the
user sessions.
To overcome these limitations, Dell EMC Networking OS provides RADIUS extension commands in order to enable unsolicited messages
to be sent to the NAS. These extension commands provide support for Disconnect Messages (DMs) and Change-of-Authorization (CoA)
packets. DMs cause user sessions to be terminated immediately; whereas, CoA packets modify session authorization attributes such as
VLAN IDs, user privileges, and so on.
Change of Authorization (CoA) packets
Using the CoA packets, the NAS can handle authorization of dot1x sessions by processing the following requests from the Dynamic
Authorization Client (DAC): Re-authentication of the supplicant, Port disable, and Port bounce.
The CoA packets constitute one message request (CoA request) and one of the following two possible responses:
• Change of Authorization Acknowledgement (CoA-Ack) - If the authorization state change is successful, then NAS sends a CoA-Ack.
• Change of Authorization non-Acknowledgement (CoA-Nak) - If the authorization state change is not successful, then the NAS sends
a CoA-Nak, which is a negative acknowledgement.
Disconnect Messages
Using the Disconnect Messages, the NAS can disconnect AAA and dot1x sessions. NAS can disconnect AAA sessions using either
username or a combination of the username and session id. NAS can disconnect dot1x sessions using NAS-port, or calling-station ID, or
both.
The disconnect messages constitue one message request (DM request) and one of the following two possible responses:
• Disconnect Acknowledgement (DM-Ack) - If the session is disconnected successfully, then NAS sends a DM-Ack.
• Disconnect non-Acknowledgement (DM-Nak) - If the session is not disconnected successfully, then NAS sends a DM-Nak.
Attributes
In Disconnect messsage requests and CoA-Request packets, certain attributes are used to uniquely identify the NAS as well as user
sessions on the NAS.
The combination of NAS and session identification attributes included in a CoA-request or a disconnect-message request must match at
least one session in order for a request to be successful; otherwise, a disconnect-Nak or CoA-Nak is sent. For disconnect-user operations
using DMs, if all NAS identification attributes match, and more than one session matches all of the session identification attributes, then a
CoA-request or a disconnect-message request applies to all matching sessions.
The following tables describe the various types of attributes that identify the NAS and the user sessions:
Table 91. NAS Identification Attributes
Attribute
code
Attribute Description
4 NAS-IP-Address IPv4 address of the NAS.
95 NAS-IPv6–Address IPv6 address of the NAS.
Table 92. Change of Authorization (CoA) Attribute
Attribute
code
Attribute Description
5 NAS-Port Port associated with the session to be processed for EAP or MAB users or the VTY ID for
AAA sessions.
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