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xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
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Access Authentication Control
The TACACS/XTACACS/TACACS+/RADIUS commands allow users to secure access to the Switch using the
TACACS/XTACACS/TACACS+/RADIUS protocols. When a user logs in to the Switch or tries to access the administrator level
privilege, he or she is prompted for a password. If TACACS/XTACACS/TACACS+/RADIUS authentication is enabled on the
Switch, it will contact a TACACS/XTACACS/TACACS+/RADIUS server to verify the user. If the user is verified, he or she is
granted access to the Switch.
There are currently three versions of the TACACS security protocol, each a separate entity. The Switch's software supports the
following versions of TACACS:
• TACACS (Terminal Access Controller Access Control System) - Provides password checking and authentication, and
notification of user actions for security purposes utilizing via one or more centralized TACACS servers, utilizing the
UDP protocol for packet transmission.
• Extended TACACS (XTACACS) - An extension of the TACACS protocol with the ability to provide more types of
authentication requests and more types of response codes than TACACS. This protocol also uses UDP to transmit
packets.
• TACACS+ (Terminal Access Controller Access Control System plus) - Provides detailed access control for
authentication for network devices. TACACS+ is facilitated through Authentication commands via one or more
centralized servers. The TACACS+ protocol encrypts all traffic between the Switch and the TACACS+ daemon, using
the TCP protocol to ensure reliable delivery
In order for the TACACS/XTACACS/TACACS+/RADIUS security function to work properly, a
TACACS/XTACACS/TACACS+/RADIUS server must be configured on a device other than the Switch, called an Authentication
Server Host and it must include usernames and passwords for authentication. When the user is prompted by the Switch to enter
usernames and passwords for authentication, the Switch contacts the TACACS/XTACACS/TACACS+/RADIUS server to verify,
and the server will respond with one of three messages:
• The server verifies the username and password, and the user is granted normal user privileges on the Switch.
• The server will not accept the username and password and the user is denied access to the Switch.
• The server doesn't respond to the verification query. At this point, the Switch receives the timeout from the server and
then moves to the next method of verification configured in the method list.
The Switch has four built-in Authentication Server Groups, one for each of the TACACS, XTACACS, TACACS+ and RADIUS
protocols. These built-in Authentication Server Groups are used to authenticate users trying to access the Switch. The users will
set Authentication Server Hosts in a preferable order in the built-in Authentication Server Groups and when a user tries to gain
access to the Switch, the Switch will ask the first Authentication Server Hosts for authentication. If no authentication is made, the
second server host in the list will be queried, and so on. The built-in Authentication Server Groups can only have hosts that are
running the specified protocol. For example, the TACACS Authentication Server Groups can only have TACACS Authentication
Server Hosts.
The administrator for the Switch may set up six different authentication techniques per user-defined method list
(TACACS/XTACACS/TACACS+/RADIUS/local/none) for authentication. These techniques will be listed in an order preferable,
and defined by the user for normal user authentication on the Switch, and may contain up to eight authentication techniques.
When a user attempts to access the Switch, the Switch will select the first technique listed for authentication. If the first technique
goes through its Authentication Server Hosts and no authentication is returned, the Switch will then go to the next technique listed
in the server group for authentication, until the authentication has been verified or denied, or the list is exhausted.
Please note that when the user logins to the device successfully through TACACS/XTACACS/TACACS+server or none method,
the “user” privilege level is the only level assigned. If the user wants to get the administration privilege level, the user must use
the “enable admin” command to promote his privilege level. However when the user logins to the device successfully through the
RADIUS server or through the local method, 3 kinds of privilege levels can be assigned to the user and the user can not use the
“enable admin” command to promote to the admin privilege level.
NOTE: TACACS, XTACACS and TACACS+ are separate entities and are not
compatible. The Switch and the server must be configured exactly the same, using the
same protocol. (For example, if the Switch is set up for TACACS authentication, so must
be the host server.)