- Telnet remotely connects to each device to centrally manage and maintain these network devices.
Telnet application scenarios
- Telnet can centrally manage local and remote network devices through the terminal.
- Telnet provides an interactive operation interface that allows terminals to remotely log in to any device that can act as a Telnet server. Telnet users can operate the device just like logging in locally through the console port. There is no need for a direct connection between the remote Telnet server and the terminal, just ensure that the two can communicate with each other. By using Telnet, users can easily manage and maintain the device remotely.
Telnet connection
- Telnet clients and servers transfer commands over TCP connections.
- Telnet operates in client / server mode. Telnet is based on the TCP protocol. The default server port number is 23. The server establishes a Telnet connection with the client through this port .
Authentication mode
- When configuring the Telnet login user interface, you must configure the authentication method, otherwise users cannot successfully log in to the device.
- Telnet authentication has two modes: AAA mode and password mode.
1.
When the authentication method of the user interface is configured as
AAA
, users need to enter the login username and password before logging in to the device.
2.
When the authentication method of the user interface is configured as
password
, users need to enter the login password first before logging in to the device.
Telnet configuration
- As a Telnet server, the network device usually uses a password authentication mechanism to authenticate users connected to the VTY interface.
- VTY ( Virtual Type Terminal ) is an interface used by network equipment to manage and monitor users who log in through Telnet . The network device assigns a VTY interface to each Telnet user . By default, the maximum number of Telnet users supported by ARG3 series routers is 5. VTY 0 4 means VTY0 , VTY1 , VTY2 , VTY3 , and VTY4 . If you need to increase the number of Telnet user logins, you can use the user-interface maximum- vty command to adjust the number of VTY interfaces.
- Run the authentication-mode password command to configure VTY to authenticate users through passwords.
- Note: There are differences in the execution of the set authentication password cipher command in different VRP versions : some platforms require you to enter the password after pressing Enter, while other platforms can enter the password directly after the command. Therefore, please refer to the corresponding VRP product documentation when operating specific products .
- After the remote device is configured as a Telnet server, you can execute the telnet command on the client to establish a Telnet connection with the server. The client will receive a prompt message related to the need for authentication. The authentication password entered by the user needs to match the password saved on the Telnet server. After passing the authentication, the user can remotely connect to the Telnet server through Telnet and configure and manage the remote device locally.
Real and complete configuration case of telnet application
Chapter summary
Q: If the network device has been configured with Telnet service, but the user still cannot achieve remote access, what may be the reason ?
Answer: If the Telnet connection cannot be established, first verify whether the device is reachable. If the device is reachable, check whether the password entered by the user is correct. If the password is correct, check whether the number of users currently accessing the device through Telnet reaches the maximum limit. If you need 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.