How Extreme Switches Work with RADIUS Servers

When configured for use with a RADIUS server, an ExtremeXOS switch operates as a RADIUS client. In RADIUS server configuration, the client component is configured as a client or as a Network Access Server (NAS). Typically, an ExtremeXOS NAS provides network access to supplicants such as PCs or phones.

When a supplicant requests authentication from a switch that is configured for RADIUS server authentication, the following events occur:

  1. The switch sends an authentication request in the form of a RADIUS Access-Request message.
  2. The RADIUS server looks up the user in the users file.
  3. The RADIUS server accepts or rejects the authentication and returns a RADIUS Access-Accept or Access-Reject message.


    A user rejected by the Radius/TACACS server can not be authenticated via local database.
  4. If authentication is accepted, the Access-Accept message can contain standard RADIUS attributes and Vendor Specific Attributes (VSAs) that can be used to configure the switch.
  5. If authentication is accepted, the Access-Accept message can enable command authorization for that user on the switch. Command authorization uses the RADIUS server to approve or deny the execution of each command the user enters.

The ExtremeXOS switch initiates all communications with the RADIUS server. For basic authentication, the switch sends the Access-Request message, and communications with the RADIUS server is complete when the switch receives the Access-Accept or Access-Reject message. For command authorization, communications starts each time a user configured for command authorization enters a switch command. RADIUS server communications ends when command use is allowed or denied.

A key component of RADIUS server management is the attributes and VSAs that the RADIUS server can be configured to send in Access-Accept messages. VSAs are custom attributes for a specific vendor, such as Extreme Networks. These attributes store information about a particular user and the configuration options available to the user. The RADIUS client in ExtremeXOS accepts these attributes and uses them to configure the switch in response to authentication events. The RADIUS server does not process attributes; it simply sends them when authentication is accepted. It is the switch that processes attributes.

User authentication and attributes are managed on a RADIUS server by editing text files. On the FreeRADIUS server, the user ID, password, attributes, and VSAs are stored in the users file, and VSAs are defined in the dictionary file. The dictionary file associates numbers with each attribute. When you edit the users file, you specify the text version of each attribute you define. When the RADIUS server sends attributes to the switch, it sends the attribute type numbers to reduce the network load. Some attribute values are sent as numbers too.

Command authorization is also managed on a RADIUS server by editing text files. On a FreeRADIUS server, the profiles file is divided into sections called profiles. Each profile lists command access definitions. In the users file, you can use the Profile-Name attribute to select the command profile that applies to each user managed by command authorization.

The ExtremeXOS software supports backup authentication and authorization by eight total servers for redundancy.

RADIUS servers can be optionally configured to work with directory services such as LDAP or Microsoft Active Directory. Because ExtremeXOS switches operate with RADIUS servers, they can benefit from the pairing of the RADIUS server and a directory service. Some guidelines for configuring FreeRADIUS with LDAP are provided later in this chapter. Since the use of the directory service requires configuration of the RADIUS server and directory service, the appropriate documentation to follow is the documentation for those products.