23.hcna-hntd--telnet principle and Configuration

If you have one or more network devices in your corporate network that need to be configured and managed remotely, administrators can use Telnet to connect to each device remotely to centralize the management and maintenance of these networked devices

Learning Goals
1. Mastering the application scenario of Telnet
2. Master how Telnet works
3. Master the basic configuration of Telnet

Telnet application Scenario

Telnet provides an interactive interface that allows the terminal to Telnet to any device that can act as a Telnet server. Telnet users can operate on the device as if they were logged on locally through the console port. There is no direct connection between the remote Telnet server and the terminal, just make sure that they can communicate with each other. By using Telnet, users can conveniently implement remote management and maintenance of the device.

Telnet connection

Telnet runs in client/server mode. Telnet is based on the TCP protocol, the server port number is 23 by default, and the server establishes a Telnet connection to the client through that port.

Authentication Mode

When you configure the Telnet logon user interface, you must configure the authentication method or the user cannot successfully log on to the device.
There are two modes of Telnet authentication: AAA mode, password mode.
1. When the authentication mode of the user interface is AAA, the user must first lose the device when logging in
Login user name and password to log in.
2. When the configuration user interface is authenticated in password, the user must first enter the login password to log in when logging on to the device.

Telnet configuration

As a Telnet server, network devices typically use a password authentication mechanism to authenticate users connected to the Vty interface.
VTY (Virtual Type Terminal) is the interface that network devices use to manage and monitor users who log on via Telnet. The network device assigns a vty interface to each telnet user. By default, the maximum number of Telnet users supported by the ARG3 series routers is 5, and VTY 0 4 means vty0,vty1,vty2,vty3,vty4. If you need to increase the number of logins for Telnet users, you can use the User-interface maximum-vty command to adjust the number of vty interfaces.
Execute the authentication-mode password command to configure the vty to authenticate the user with a password.

After the remote device is configured as a Telnet server, the telnet command can be executed on the client to establish a Telnet connection to the server. The client receives a message that requires authentication, and the authentication password entered by the user needs to match the password saved on the Telnet server. After authentication, the user can remotely connect to the Telnet server via Telnet and configure and manage the remote device locally.

Summarize

If the network device has been configured to complete the Telnet service, but the user still cannot achieve remote access, what could be the reason?
For:
If you are unable to establish a Telnet connection, first verify that the device is unreachable. If the device is up, then check that the user entered the correct password. If the password is correct, then see if the maximum number of users currently accessing the device via Telnet is reached. To increase the number of users, you can execute the user-interface maximum-vty <0-15> command, 0-15 indicates the number of supported users.

23.hcna-hntd--telnet principle and Configuration