The authentication mode must be specified on the device; otherwise, users cannot log in to the device through Telnet. The device supports non-authentication, password authentication, and AAA authentication, in which AAA authentication has the highest security.

To authenticate the Telnet users through AAA, enable the Telnet service on the device, set the authentication mode of the user interface (for example, VTY) to aaa, create a local account in the AAA view, and set the user access type and user level.

<HUAWEI> system-view
[HUAWEI] telnet server enable  //Enable the Telnet service.
[HUAWEI] user-interface maximum-vty 15  //Set the maximum number of VTY login users to 15.
[HUAWEI] user-interface vty 0 14  //Enter the view of VTY users at level 0-14.
[HUAWEI-ui-vty0-14] authentication-mode aaa  //Set the VTY authentication mode to AAA. 
[HUAWEI-ui-vty0-14] protocol inbound telnet  //By default, switches in V200R006 and earlier versions support Telnet, and switches in V200R007 and later versions support SSH.
[HUAWEI-ui-vty0-14] quit
[HUAWEI] aaa
[HUAWEI-aaa] local-user user1 password irreversible-cipher Huawei@1234  //Create the local user user1 and set the password. The password is displayed in cipher text in the configuration file, so remember the password. If you forget the password, run this command again to overwrite the old configuration.
[HUAWEI-aaa] local-user user1 service-type telnet  //Set the access type of user1 to Telnet. This user can only log in to the device through Telnet.
[HUAWEI-aaa] local-user user1 privilege level 15  //Set the user level of user1 to 15. After login, the user can run the commands at level 0-15.
[HUAWEI-aaa] quit