Cisco Systems 4.2 manual Separation of Administrative and General Users

Chapter 2 Deploy the Access Control Servers

Additional Topics

A small network with a small number of network devices may require only one or two individuals to administer it. Local authentication on the device is usually sufficient. If you require more granular control than what authentication can provide, some means of authorization is necessary. As discussed earlier, controlling access by using privilege levels can be cumbersome. ACS reduces this problem.

In large enterprise networks, with many devices to administer, the use of ACS practically becomes a necessity. Because administration of many devices requires a larger number of network administrators, with varying levels of access, the use of local control is simply not a viable way to track network-device configuration changes that are required when changing administrators or devices.

The use of network management tools, such as CiscoWorks, helps to ease this burden; but, maintaining security is still an issue. Because ACS can comfortably handle up to 300,000 users, the number of network administrators that ACS supports is rarely an issue. If a large remote-access population is using RADIUS for AAA support, the corporate IT team should consider separate TACACS+ authentication by using ACS for the administrative team. Separate TACACS+ authentication would isolate the general user population from the administrative team and reduce the likelihood of inadvertent access to network devices. If the use of TACACS+ is not a suitable solution, using TACACS+ for administrative (shell or exec) logins, and RADIUS for remote network access, provides sufficient security for the network devices.

Separation of Administrative and General Users

You should prevent the general network user from accessing network devices. Even though the general user may not intend to gain unauthorized access, inadvertent access could accidentally disrupt network access. AAA and ACS provide the means to separate the general user from the administrative user.

The easiest and recommended method to perform such separation is to use RADIUS for the general remote-access user and TACACS+ for the administrative user. One issue is that an administrator may also require remote network access, like the general user. If you use ACS, this issue poses no problem. The administrator can have RADIUS and TACACS+ configurations in ACS. By using authorization, RADIUS users can set PPP (or other network access protocols) as the permitted protocol. Under TACACS+, only the administrator would be configured to have shell (exec) access.

For example, if the administrator is dialing in to the network as a general user, a AAA client would use RADIUS as the authenticating and authorizing protocol, and the PPP protocol would be authorized. In turn, if the same administrator remotely connects to a AAA client to make configuration changes, the

AAAclient would use the TACACS+ protocol for authentication and authorization. Because this

administrator is configured on ACS with permission for shell under TACACS+, the administrator would be authorized to log in to that device. This does require that the AAA client have two separate configurations on ACS, one for RADIUS and one for TACACS+.

An example of a AAA client configuration under IOS that effectively separates PPP and shell logins is:

aaa new-model		ip-address
tacacs-server	host
tacacs-server	key	secret-key
radius-server	host	ip-address
radius-server	key	secret-key
aaa authentication		ppp default group radius

aaaauthentication login default group tacacs+ local aaa authentication login console none

aaa authorization network default group radius aaa authorization exec default group tacacs+ none

aaaauthorization command 15 default group tacacs+ none username user password password

line con 0

login authentication console

	Configuration Guide for Cisco Secure ACS 4.2
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