The TACACS+ protocol supports accounting as a function that is distinctly separate from authentication. You can use TACACS+ for authentication only, for accounting only, or for both. With a TACACS+ server you can track user logins and the commands that users run during a login session by enabling login accounting, command accounting, or both.
When a TACACS+ server is used for authentication, authorization, or accounting, the device attempts to connect to the first TACACS+ server configured in the list. When the first TACACS+ server cannot be reached, the device attempts to send the packets to the next server on the list.
Note
When the first server on the list is reachable again, the device sends packets to the first server.