Historical runs under the Microsoft Telnet
Client from a router.|alt=Screenshot of a black screen with the output of the help command and a # prompt. Historically, Telnet provided access to a
command-line interface on a remote host. However, because of serious security concerns when using Telnet over an open network such as the Internet, its use for this purpose has waned significantly in favor of
SSH. The usage of Telnet for remote management has declined rapidly, especially on the public
Internet, in favor of the
Secure Shell (SSH) protocol. SSH provides much of the functionality of telnet, with the addition of strong encryption to prevent sensitive data such as passwords from being intercepted, and
public key authentication, to ensure that the remote computer is actually who it claims to be.
Modern The Telnet protocol is mainly used for legacy equipment that does not support more modern communication mechanisms. For example, many industrial and scientific devices only have Telnet available as a communication option. Some are built with only a standard
RS-232 port and use a serial server hardware appliance to provide the translation between the TCP/Telnet data and the RS-232 serial data. In such cases, SSH is not an option unless the interface appliance can be configured for SSH (or is replaced with one supporting SSH). Telnet support has become highly unusual in new applications, though
amateur radio operators and
multi-user dungeons do continue to utilize it. Security researchers estimated that 7,096,465 exposed systems on the Internet continue to use Telnet as of 2021. However, estimates of this number have varied significantly, depending on the number of ports scanned beyond the default TCP port 23. ==Technical details==