ogin authentication NS-OS requires usernames. This behavior cannot be disabled. As such, there is no need to add the login command to VTY or CON interfaces. You also cannot assign a pass- word to the console or VTYs as you can in IOS. You can, however, tell NX-OS to use RADIUS or TACACS+ for user authentication. The command is the same as the one we used in IOS: NX-7K-1-Cozy(config)# aaa authentication login default group Login-Servers none PPP authentication PPP authentication is used when Point-to-Point Protocol connections are initiated into the router. These can include modem connections into a serial interface or connections of high-speed serial links such as T1s. AAA Authentication The possible methods for PPP authentication using AAA are: if-needed If a user has already been authenticated on a TTY line, do not authenticate. Query a Kerberos 5 authentication server for authentication information (only for PAP). local Use locally configured usernames and passwords (entered in the configuration of the device itself). local-case Same as local, but the usernames are case-sensitive. This method essentially removes authentication. If none is the only method, there is no challenge. group radius Query the list of RADIUS servers for authentication information. group tacacs+ Query the list of TACACS+ servers for authentication information Custom (group group-name) Query a custom group as defined in the local configuration. These methods are referenced in ppp method lists the same way methods are referenced in login method lists. An interesting addition to the list of methods is if-needed. This method instructs the router to authenticate the incoming connection only if the user has not already been authenticated on a VTY, console, or aux line. Here is a sample ppp method list: aaa authentication ppp default group tacacs+ local-case Applying Method Lists Once you have created a method list, you need to apply it to the interface or line where you would like it to take effect. With login authentication, use the command l