Based on a user ID and password combination, authentication, authorization, and accounting (AAA) is used to authenticate and authorize users. A key secures communication with AAA servers. AAA supports IPv4 addresses.

In many circumstances, AAA uses protocols such as RADIUS or TACACS+ to administer its security functions. If your router or access server is acting as a network access server, AAA is the means through which you establish communication between your network access server and your RADIUS or TACACS+ security server.

Although AAA is the primary (and recommended) method for access control, additional features for simple access control are available outside the scope of AAA, such as local username authentication, line password authentication, and enable password authentication. However, these features do not provide the same degree of access control that is possible by using AAA.

Separate AAA configurations are made for the following services:

• User Telnet or Secure Shell (SSH) login authentication

• Console login authentication

• User management session accounting

The following table provides the authentication commands:

Authentication provides the method of identifying users, including login and password dialog, challenge and response, messaging support, and, depending on the security protocol that you select, encryption. Authentication is the way a user is identified prior to being allowed access to the network and network services. You configure AAA authentication by defining a named list of authentication methods and then applying that list to various interfaces.

Authentication is accomplished as follows:

The following figure shows a flowchart of the authentication process.

Figure 1. Authenticating User Login

Note	This diagram is applicable only to username password SSH authentication. It does not apply to public key SSH authentication. All username password SSH authentication goes through AAA.

Authorization restricts the actions that a user is allowed to perform. It provides the method for remote access control, including one-time authorization or authorization for each service, per-user account list and profile, user group support, and support of IP, IPX, ARA, and Telnet.

Remote security servers, such as RADIUS and TACACS+, authorize users for specific rights by associating attribute-value (AV) pairs, which define those rights, with the appropriate user. AAA authorization works by assembling a set of attributes that describe what the user is authorized to perform. These attributes are compared with the information contained in a database for a given user, and the result is returned to AAA to determine the user’s actual capabilities and restrictions.

Accounting provides the method for collecting and sending security server information used for billing, auditing, and reporting, such as user identities, start and stop times, executed commands (such as PPP), number of packets, and number of bytes. Accounting enables you to track the services that users are accessing, as well as the amount of network resources that they are consuming.

Accounting tracks and maintains a log of every SVS management session. You can use this information to generate reports for troubleshooting and auditing purposes. You can store accounting logs locally or send them to remote AAA servers.

Remote AAA server groups can provide failovers if one remote AAA server fails to respond, which means that if the first server in the group fails, the next server in the group is tried until a server responds. Multiple server groups can provide failovers for each other in this same way.

If all remote server groups fail, the local database is used for authentication.

• At least one TACACS+ or RADIUS server is IP reachable

• The VSM is configured as an AAA server client.

• A shared secret key is configured on the VSM and the remote AAA server.

The Cisco Nexus 1000V does not support usernames that have all numeric characters and does not create local usernames that have all numeric characters. If a username that has all numeric characters already exists on an AAA server and is entered during login, the Cisco Nexus 1000V does authenticate the user.