Managing Authentication Servers TACACS+ Server
OmniSwitch AOS Release 8 Network Configuration Guide December 2017 page 31-13
TACACS+ Server
Terminal Access Controller Access Control System (TACACS+) is a standard authentication and
accounting protocol defined in RFC 1321 that employs TCP for reliable transport. A built-in TACACS+
client is available in the switch. A TACACS+ server allows access control for routers, network access
servers, and other networked devices through one or more centralized servers. The protocol also allows
separate authentication, authorization, and accounting services. By allowing arbitrary length and content
authentication exchanges, it allows clients to use any authentication mechanism.
The TACACS+ client offers the ability to configure multiple TACACS+ servers. This can be done by the
user. When the primary server fails, the client tries the subsequent servers. Multiple server configurations
are applicable only for backup and not for server chaining.
In the TACACS+ protocol, the client queries the TACACS+ server by sending TACACS+ requests. The
server responds with reply packets indicating the status of the request.
• Authentication. TACACS+ protocol provides authentication between the client and the server. It also
ensures confidentiality because all the exchanges are encrypted. The protocol supports fixed
passwords, one-time passwords, and challenge-response queries. Authentication is not a mandatory
feature, and it can be enabled without authorization and accounting. During authentication if a user is
not found on the primary TACACS+ server, the authentication fails. The client does not try to
authenticate with the other servers in a multiple server configuration. If the authentication succeeds,
then Authorization is performed.
• Authorization. Enabling authorization determines if the user has the authority to execute a specified
command. TACACS+ authorization cannot be enabled independently. The TACACS+ authorization is
enabled automatically when the TACACS+ authentication is enabled.
• Accounting. The process of recording what the user is attempting to do or what the user has done is
Accounting. The TACACS+ accounting must be enabled on the switches for accounting to succeed.
Accounting can be enabled irrespective of authentication and authorization. TACACS+ supports three
types of accounting:
Start Records—Indicate the service is about to begin.
Stop Records—Indicates the services has just terminated.
Update Records—Indicates the services are still being performed.
TACACS+ Client Limitations
The following limitation apply to this implementation of the TACACS+ client application:
• TACACS+ supports Authenticated Switch Access and cannot be used for user authentication.
• Authentication and Authorization are combined together and cannot be performed independently.
• On the fly, command authorization is not supported. Authorization is similar to the AOS partition
management families.
• Only inbound ASCII logins are supported.
• A maximum of 50 simultaneous TACACS+ sessions can be supported when no other authentication
mechanism is activated.
• Accounting of commands performed by the user on the remote TACACS+ process is not supported in
the boot.cfg file at boot up time.
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