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Understanding Telnet

Updated: March 24, 2010

Applies To: Windows 7, Windows 8, Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Vista

Telnet is an Internet-standard program and protocol based on Request for Comments (RFC) 854. This RFC specifies a method for transmitting and receiving unencrypted ASCII characters (plaintext) across a network.

Telnet consists of two services: Telnet Client and Telnet Server. You can use a Telnet client running on one computer to use a command line-based session to run applications on a computer on a remote network that is running the Telnet Server service. Only character-based interfaces and applications are supported. There is no graphics capability in the Telnet environment.

Telnet Client allows a computer to connect to a remote Telnet server and run applications on that server. After the client is logged on, a user is given a command prompt that can be used as if it had been opened locally on the Telnet server. Only programs that work with the command prompt and that do not interact with the desktop or use a graphical user interface work with Telnet.

All members of the Windows® 7, Windows Server® 2008 R2, Windows Server® 2008, and Windows Vista® operating system families include Telnet Client, but it is not installed by default. For more information about installing the Telnet Client service, see Install Telnet Client.

Telnet Server hosts the remote sessions for Telnet clients. When Telnet Server is running on a computer, users can connect to the Telnet server by using a remote computer running Telnet Client. Telnet Server is implemented in Windows as a service that can be configured to always run, even when no one is logged on to the server.

When a Telnet client connects to a computer running Telnet Server, the remote user is asked to enter a user name and password. The user name and password combination must be one that is valid on the Telnet server. Telnet Server supports two types of authentication: NTLM and Password (or plaintext). For more information, see Configure Telnet Server Authentication.

After logging on, a user sees a command prompt that can be used like a command prompt on their local computer. Commands that you type at the Telnet Client command prompt are sent to the Telnet server and run there, as though you were locally logged on to a command prompt session at the server. Output from the commands you run are displayed in the command prompt window on the Telnet client.

Telnet does not support applications that require a graphical user interface. However, Telnet Server and Telnet Client support special character sequences that provide some level of formatting and cursor positioning within the Telnet Client window. Telnet Server and Telnet Client support the emulation of four types of terminals: ANSI, VT-100, VT-52, and VT-NT.

Windows 7, Windows Server 2008 R2, Windows Vista, and Windows Server 2008 include Telnet Server, but it is not installed by default. For more information about installing the Telnet Server service, see Install Telnet Server.

For additional information about the standards that define Telnet, see the following documents available at the Internet Engineering Task Force Web site (http://go.microsoft.com/fwlink/?linkid=121):

  • RFC 854: Telnet Protocol Specification

  • RFC 2839: Internet Kermit Service

  • RFC 2877: 5250 Telnet Enhancements

  • RFC 2941: Telnet Authentication Option

  • RFC 4248: The Telnet URI Scheme

  • RFC 4559: SPNEGO-based Kerberos and NTLM HTTP Authentication in Microsoft Windows

See Also

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