The TACACS+ protocol provides authentication between the switch and the TACACS+ daemon, and it
ensures confidentiality because all protocol exchanges between the switch and the TACACS+ daemon are
encrypted.
Related Topics
Prerequisites for TACACS+, on page 39
TACACS+ Operation
When a user attempts a simple ASCII login by authenticating to a switch using TACACS+, this process occurs:
1
When the connection is established, the switch contacts the TACACS+ daemon to obtain a username
prompt to show to the user. The user enters a username, and the switch then contacts the TACACS+
daemon to obtain a password prompt. The switch displays the password prompt to the user, the user enters
a password, and the password is then sent to the TACACS+ daemon.
TACACS+ allows a dialog between the daemon and the user until the daemon receives enough information
to authenticate the user. The daemon prompts for a username and password combination, but can include
other items, such as the user’s mother’s maiden name.
2
The switch eventually receives one of these responses from the TACACS+ daemon:
• ACCEPT—The user is authenticated and service can begin. If the switch is configured to require
authorization, authorization begins at this time.
• REJECT—The user is not authenticated. The user can be denied access or is prompted to retry the
login sequence, depending on the TACACS+ daemon.
• ERROR—An error occurred at some time during authentication with the daemon or in the network
connection between the daemon and the switch. If an ERROR response is received, the switch
typically tries to use an alternative method for authenticating the user.
• CONTINUE—The user is prompted for additional authentication information.
After authentication, the user undergoes an additional authorization phase if authorization has been enabled
on the switch. Users must first successfully complete TACACS+ authentication before proceeding to
TACACS+ authorization.
3
If TACACS+ authorization is required, the TACACS+ daemon is again contacted, and it returns an
ACCEPT or REJECT authorization response. If an ACCEPT response is returned, the response contains
data in the form of attributes that direct the EXEC or NETWORK session for that user and the services
that the user can access:
•
Telnet, Secure Shell (SSH), rlogin, or privileged EXEC services
•
Connection parameters, including the host or client IP address, access list, and user timeouts
Related Topics
Prerequisites for TACACS+, on page 39
Catalyst 2960-X Switch Security Configuration Guide, Cisco IOS Release 15.0(2)EX
OL-29048-01 43
Configuring TACACS+
TACACS+ Operation
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