Telnet Telnet is a network protocol established in 1974 that is based on character-oriented data exchange over a TCP connection. It is available on all common operating systems and therefore also enables exchange between different operating systems. Secure remote access to computers with Telnet The Telnet client establishes an unencrypted connection to a remote computer. An encrypted connection can be established using SSH. This makes it possible to open a command line on a remote computer. Before the connection can be established, the user is prompted to enter a username and password combination. The password is then passed during the connection process. If the data allows access, the Telnet protocol can be initiated. As soon as a connection has been established between the Telnet client and the Telnet server, text-based input is transmitted. The remote computer then returns the output of a programme in text form. Nowadays, Telnet is primarily used for connection tests due to security vulnerabilities. Nevertheless, Telnet is also used for database queries and remote configuration. Telnet commands WILL (251): offer or acceptance to enable WON’T (252): acceptance of the offer to disable DO (253): request or authorise to enable operation DON’T (254): do not authorise release or request deactivation SE (240): end of sub-negotiation parameters NOP (241): No operation DM (242): Data marking BRK (243): Break command IP (244): Interruption of the connection AO (245): Abort output AYT (246): ‘Are you there?’ command All terms in Expert Know-how