Multiple Backup Systems

AAA supports multiple security servers, such as TACACS+, on the same network to provide redundancy in case of device failure or link congestion. In addition, AAA allows for multiple authentication methods to be specified so, if the first one is unavailable, then a second or third option could be used. For example, if the specified TACACS+ server is offline, the locally stored user name/password database could possibly be used or maybe even the enable password. These alternatives must be defined in advance or access could be blocked until the specified service is restored.