 the hostnames and passwords in odd ways. Instead, you configure the username and password using the ppp chap interface commands on the calling side. The called side simply has the username and password configured to match. The hostnames, while included for com- pletion, are not necessary in this example (though they are in all the previous CHAP examples). Of all the non-AAA authentication methods available for PPP, this is the most secure and the easiest to understand. AAA Authentication Recall that AAA stands for Authentication, Authorization, and Accounting. Authenti- cation is the process of verifying a user's identity to determine whether the user should be allowed access to a device. Authorization is the act of limiting or permitting access to certain features within the device once a user has been authenticated. Accounting is the recording of actions taken by the user once she has been authenticated and thorized. In this section, I will cover only authentication, as it is the most commonly used feature offered by AAA. To use AAA authentication on an IOS switch or router, you must perform the following steps: 1. Enable AAA by entering the aaa new-model command. 2. Configure security server information, if you're using a security server. This step includes configuring TACACS+ and RADIUS information. 3. Create method lists by using the aaa authentication command. 4. Apply the method lists to interfaces or lines as needed. In NX-OS, the commands are similar, but there is no aaa new-model command. Enabling AAA To use the AAA features discussed here, you'll need to issue the command aaa new-model: er(config)#aa new-model AAA Authentication If you don't execute this command, the AAA commands discussed in this section will not be available. This step is not necessary in NX-OS. Be careful when configuring AAA for the first time. You can easily lock yourself out of the router by enabling AAA authentication without con- figuring any users. Configuring Security Server Information One of the benefits of using AAA is th