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Introduction to Telnet

Telnet uses the TELNET protocol (part of the TCP/IP protocol suite) to connect to a remote computer over the network. The Telnet client software allows a computer to connect to a remote computer. The Telnet server software allows Telnet clients to connect to a server, login to that server, and run character-mode applications.


Telnet Licensing

When using Telnet on Windows NT Server, the licensing is integrated with the Windows NT licensing pool. When using Telnet on Windows NT Workstation computers, only one Telnet connection is permitted.


Using Telnet

Telnet can be accessed either by using a graphical user interface, which is provided with Windows NT, or from a command line. Windows NT Services for UNIX Add-on Pack provides a command line Telnet client and Telnet server. The Telnet client works with other Telnet servers, such as the Microsoft Telnet server supplied with Windows NT and UNIX-based Telnet servers. The Telnet server works with other Telnet clients, such those supplied with Windows 95 and Windows NT, and UNIX-based Telnet clients. The Telnet server uses Windows NT LAN Manager (NTLM) for authentication and provides a VTNT terminal emulation option. The command line interface offers scripting capabilities.

The VTNT terminal type can be used only when both your Telnet client and Telnet server support the VTNT terminal type.

VTNT is the preferred terminal type if you need to use advanced native character-mode applications such as edit.exe while communicating between Windows NT Services for UNIX Add-on Pack Telnet client and server computers.


Start the Telnet server provided with Windows NT
To start the Telnet server provided with Windows NT

1.	From the Control Panel, click Services and then select Microsoft Telnet Service.

2.	Click Startup.


Stop the Telnet server provided with Windows NT
To stop the Telnet server provided with Windows NT

1.	From the Control Panel, click Services and then select Microsoft Telnet Service.

2.	Click Stop.


Logging Into Telnet
Authentication

You can use your local Windows NT user name and password or domain account information to access the Telnet server. The security scheme is integrated into Windows NT security.

If you do not use the Windows NT LAN Manager (NTLM) authentication option, the user name and password is sent to the Telnet server as plain text.

If you are using NTLM authentication, the client uses the Windows NT security context for authentication and the user is not prompted for a user name and password. The user name and password are encrypted.

Note

•	If the password option User Must Change Password at Next Logon is set for the user, an attempt to log onto the Telnet server fails when NTLM authentication is used. The user must log onto the server directly and change their password, then log on through Telnet.


The Telnet Graphical User Interface

You can use the Telnet client graphical interface provided with Windows NT to connect to a remote computer, log onto the computer, and modify user preferences. When using the Telnet client supplied with Windows NT (telnetw.exe) with the Microsoft Telnet server, please note the following:

•	The recommended terminal type is VT100.

•	The Local Echo option is turned off by default and should not be changed.

•	The default buffer size is set to 25 and should not be changed.


Stop the Telnet service from the command line
To stop the Telnet service from the command line

•	Type net stop tlntsvr


Start the Telnet service from the command line
To start the Telnet service from the command line

•	Type net start tlntsvr


Start the GUI client from the command line
To start the Telnet client supplied with Windows NT from the command line

•	Type telnetw


Access Telnet from the command line
To access Telnet from the command line

•	Once the service is started, type telnet [hostname] [port#]

Note

•	The port number is optional unless a port other than the default Telnet port is in use.


Telnet Commands

The following commands are available from the Microsoft Telnet> prompt. Each command can be abbreviated to the shortest possible unique string.

Command	Function
Open	Connect to site
Close	Close current connection
Display	Display operating parameters
Quit	Exit Telnet
Set	Set options (set ? for list)
Status	Print status information
Unset	Unset options (unset ? for list)
?/help	Print help information


The Open Command

The open command connects to a Telnet server.


The Close Command

The close command closes the connection to a Telnet server, but does not close the Telnet client.


The Display Command

The display command lists the current operating parameters. If you are in a Telnet session (connected to a Telnet server), to modify the parameters, press Ctrl-]. This escapes from the Telnet session. (To return to the Telnet session, press Enter.) The following operating parameters are available:

•	WILL AUTH (NTLM Authentication)

•	WONT AUTH

•	WILL TERM TYPE

•	WONT TERM TYPE

•	LOCAL_ECHO off

•	LOCAL_ECHO on


The Quit Command

The quit command closes the Telnet client.


The Set Command

You can set the following options using the set command (use ? to see a list of the options):

•	set NTLM. Makes NTLM Authentication available.

•	Set LOCAL_ECHO

•	set TERM (enter terminal type)

Terminal type options are:

•	ansi

•	vt100

•	vt52

•	vtnt

If you choose to use NTLM Authentication, you are not prompted for a logon name and password when connecting from a remote computer.

When you connect to the Microsoft Telnet server:

•	Use the VT100 terminal type if you are running normal command line applications.

•	Use the VTNT terminal type if you are running advanced command line applications such as edit.


The Status Command

The status command shows the current connection status. The two possibilities are:

•	Connected

•	Not connected


The Unset Command

You can use the unset command to turn off NTLM authentication (use ? to see a list of the options)

•	unset NTLM. This turns off NTLM authentication.

•	Unset LOCAL_ECHO

Note

•	To change terminal type settings, you must use the set command.


Editing the Registry

You may need to change certain registry settings for optimal performance. Before you edit the registry, stop the Telnet server. When you have completed your changes, you must restart the Telnet server for the changes to take effect.

Important

•	Use extreme care when you make changes in the registry. Changing the registry with a registry editor (Regedit or Regedt32) can disable your computer, so you should back up the registry before making any changes.

Note

•	You can also edit the registry using the Telnet Server Administration Utility.

The following registry settings are useful:

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, the value of AllowTrusted Domain can be either 0 or 1. The default value of 1 permits any user from a trusted domain to log on to the server. The value of 0 prohibits log on from a trusted domain.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, the value of AltKeyMapping should be changed to the appropriate mapping for the Alt key on your system. For example, a value of 1 maps the Ctrl-A key sequence to the Alt key.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, enter the name of the default domain in DefaultDomain. The default value is "." (period). A user who is a member of the default domain does not have to enter the domain name as part of the logon name.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, in DefaultShell, enter the full path name of the shell that will be used. Any shell that runs under Windows NT (for example, Korn shell, C shell) is appropriate. The default shell is cmd.exe.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, the value for LoginScript is the full path name of the cmd batch file that contains the login script and is run when a user logs on to the server.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, enter a number between 0 - 63 (inclusive) for the value of MaxConnections. In general, the number of maximum connections is either the same as the number of licenses or less, depending upon the number entered into the registry and the number available from the Windows NT license pool at a given time.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, the value of MaxFailedLogins can be any number. The default value is 3. This value determines the number of unsuccessful logons that are permitted before a failure is returned.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, the value of NTLM can be 0,1 or 2. The default value is 1. This value determines how NTLM authentication is used.

Value	Effect
0	NTLM not available
1	NTLM or login prompt. NTLM is tried before the login prompt.
2	NTLM only
Note

When the value is set to 1, there are two possibilities:

•	If the client supports NTLM, but the authentication fails, the server sends the logon prompt.

•	If the client does not support NTLM, the server sends the logon prompt.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, TelnetPort is used for the number of the internal standard port used for Telnet. The default value is 23.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0 subkey, the value of TermCap is the full path name for the location of the TERMCAP file. This file contains the necessary parameters for specific terminal types.

•	In the HKEY_LOCAL_MACHINE\SOFTWARE\MICROSOFT
\TelnetServer\1.0\Performance subkey, NumThreadsPerProcessor is set to a default of 10, which should optimize performance. The minimum value is 2.


The Telnet Server Administration Utility

You must have administrative privileges to use the Telnet Server Administration utility. Run tlntadmn.exe to gain access to the Administration utility and complete the following tasks:

•	List the users connected to the Telnet server. This displays the name and domain of each user, the name of the user’s computer, the time at which the session started, and the session ID.

•	End a certain user's Telnet session. You are prompted for the session ID of the Telnet session you wish to end.

•	Change the registry settings. You must stop and restart the Telnet server for the changes to take effect.

•	Start and stop the Telnet server.

•	Administer remote Telnet servers (using the command: tlntadmn  [\\computername]).

When you select to change registry settings, you are prompted to choose from the following registry settings to edit:

•	AllowTrustedDomain

•	AltKeyMapping

•	DefaultDomain

•	DefaultShell

•	LoginScript

•	MaxConnections

•	MaxFailedLogins

•	NTLM

•	TelnetPort

Important

•	Use extreme care when you make changes in the registry.


Telnet Server Limitations

Note:

•	The server does not prevent you from starting a graphical user interface application.


Event Log

Refer to the Event Log to monitor events for the Telnet server.


Glossary

Authentication. In a networking environment, the method used to validate a user’s logon information.

Client. A computer or program that accesses shared network resources provided by a server.

Echo. Returning input received from the keyboard to the computer screen.

Server. A computer or program that responds to requests from a client.

VT52. A terminal emulation specification that causes a computer to perform like a Digital VT52 device.

VT100. A terminal emulation specification that causes a computer to perform like a Digital VT100 device.


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The names of actual companies and products mentioned herein may be the trademarks of their respective owners.


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