Telnet is a communication protocol used to access a remote host over a TCP/IP network.
Telnet is an application layer protocol – a specific way of communicating over a network – that functions over the Internet or any other TCP/IP network. Telnet is used to establish a command-line, text-only interface on a remote host, typically called a Telnet server.
Developed in 1969, Telnet actually predates the creation of TCP/IP, and originally operated over Network Control Program (NCP) protocols. Adopted by the Internet in the 1980s, Telnet was used regularly to access web servers until the late 1990s.
Telnet is the formal name of a communication protocol and a proper noun, but it can also be used as a verb. For example, instructions for performing an operation using a Telnet client might say something like “open the application and telnet to the server”.
A Telnet client is an application designed to establish and work with a Telnet connection. Clients are available for all major operating systems, including Mac OS X, Windows, Unix, and Linux. Login credentials are typically required in order to establish a connection between the client and server. However, information, including credentials, transmitted over a Telnet connection is not encrypted.
From it's inception, Telnet presented security concerns, due to the transmission of server authentication credentials in plain text – meaning that anyone with skilled enough to sniff network connections could easily locate server access credentials. In 1995, in response to a security breach, Secure Shell (SSH) was developed, and rapidly replaced Telnet as the go-to protocol for remote access to web servers.
Frequently Asked Questions
Is Telnet still used today?
SSH has replaced Telnet for virtually all applications. However, Telnet can still be used to access a remote Telnet server over any TCP/IP network. Due to the security risks inherent to use Telnet, there is very little professional use of Telnet at this point. However, local area network administrators, hobbyists, and technology enthusiasts continue to use Telnet for a variety of purposes, including:
- Working with antiquated hardware: Legacy Unix servers and old Cisco routers may not offer support for SSH. While this hardware should not be used for highly-sensitive purposes, it may well still be in use in a private network. Telnet may be the only way to work with these legacy systems remotely.
- Text-based bulletin boards: There are several text-based bulletin boards accessible with Telnet.
- Checking the weather: Weather Underground offers access to weather forecasts with Telnet.
- Having a laugh: There are number of fun projects you can access over Telnet including a partial recreation of Star Wars Episode 4 in ASCII characters, simple games such as chess, Eliza the AI Psychotherapist who will provide insightful tongue-in-cheek answers to all of life's questions, The Bastard Operator from Hell excuse generator, and more.