Learn about Telnet protocol

Telnet is a command line protocol used to manage various devices such as servers, PCs, routers, switches, cameras, and remote firewalls. Telnet is a protocol that provides simple remote connectivity. Telnet is responsible for sending commands or data to remote network connections. This makes this protocol very popular in IT systems. Telnet often appears after SSH to manage the remote system using the command line.

Telnet's history

Telnet protocol is created by computer networks. Computer networks make computers available to manage and use remotely. Telnet was created as a remote command line interface management protocol. Telnet was first used in 1969 and designed as a simple TCP / IP protocol.

Structure

Telnet has a popular Client and Server structure. The server side (Server) will provide Telnet service to connect from Telnet applications of the client (Client). Telnet server side usually listens to TCP port 23 to accept Telnet connection. But this port may be changed for security or other reasons. Therefore, the Telnet client needs to specify the Telnet port.

Telnet features

Telnet is a simple protocol that has very few features. Telnet protocol provides the following features for remote system management.

1. Simple
2. Display connection information
3. Fast
4. Not secure

Device

As mentioned before, Telnet is a very popular protocol, which means it is used by a wide variety of devices in a wide range. Below is a list of devices that use Telnet for remote management.

1. Linux
2. Router
3. Switch
4. Firewall
5. Router
6. Camera
7. Iodine
8. Windows
9. Raspberry Pi
10. Cisco IOS

Install for Linux

As previously stated, Telnet's structure includes servers and clients. Telnet servers and clients can be installed on all Linux distributions such as Ubuntu, Debian, Fedora, CentOS, RedHat, Mint, etc.

 $ sudo apt install telnet 

Install for Windows

Telnet servers and clients can be installed into Windows or client servers in different ways. Telnet clients and servers are preinstalled on Windows. The alternative is to install 3rd party applications such as MoboTerm, etc.

Telnet security level

Telnet's security is the biggest challenge of this protocol. Telnet protocol is not encrypted so it is easy to be targeted for man-in-the-middle attacks. Telnet traffic can be exposed at any time. Telnet also only provides password-based authentication. As previously stated, passwords transmitted over the network can be stolen by attackers. Password-based authentication is less secure than certificate-based or key-based authentication.

Telnet encryption with Telnet / s

By default, the Telnet protocol does not encrypt its traffic. If you want to encrypt traffic, you can use Telnet / s. In fact, some tunnels TLS / SSL will be created and telnet traffic is transmitted through this TLS / SSL tunnel. Therefore, Telnet / s is not widely used.

Telnet alternative

There are various alternatives for Telnet. SSH is a popular and better alternative to Telnet protocol.

1. SSH provides better security by encrypting traffic and providing safer authentication. SSH also has many additional features such as desktop X forwarding, port forwarding, etc.
2. RDP is not a remote protocol using the command line, but based on the GUI. RDP needs more network bandwidth but provides a complete desktop experience.
3. VNC is an open source alternative similar to the RDP protocol. VNC provides remote desktops but is slower than RDP in most cases.
4. SNMP is designed for remote management of non-interactive commands. But SNMP is mainly used to monitor remote systems and not completely replace Telnet protocol.

Entertainment with Telnet

There are several Telnet services on the Internet that provide ASCII-based or asciinema videos. The service runs a short movie via Telnet protocol. You can access this movie from towel.blinkenlights.nl as follows:

 $ telnet towel.blinkenlights.nl 

Enjoy it!