Windows XP: Telnet Internals

The Telnet Server service values are located in the following registry key:

HKEY_LOCAL_MACHINESoftwareMicrosoftTelnetServer1.0

The possible Telnet Server registry values and data types include:

Name                   Data type         Values
--------------------------------------------------------------------------
AltKeyMapping          REG_DWORD         0x00: Press CTRL+A.
                                         This key combination emulates
                                         the ALT key. This enables you to
                                         send an ALT combination to
                                         programs running on SFU Telnet
                                         servers.

                                         0x19: Press CTRL+Z.
                                         This key combination emulates
                                         the ALT key. This enables you to
                                         send an ALT combination to
                                         programs running on SFU Telnet
                                         servers.

DefaultDomain          REG_EXPAND_SZ     Uses default Windows domain for
                                         login authentication.

DefaultShell           REG_EXPAND_SZ     Defines the full path of
                                         the shell or command
                                         interpreter that runs
                                         when a Telnet user logs
                                         on. The default is Windows NT
                                         Command Prompt (Cmd.exe), but can
                                         be set to a UNIX shell.

LoginScript            REG_EXPAND_SZ     Sets the full path of a batch
                                         file when a Telnet user logs on.
                                         This is similar to a global
                                         .cshrc file or profile in UNIX.

MaxConnections         REG_DWORD         Applies only if you
                                         purchase a license through
                                         Services for UNIX. In Windows
                                         2000, the Telnet Server service
                                         has a hard coded limit of two
                                         simultaneous connections.

MaxFailedLogins        REG_DWORD         Determines the number of
                                         unsuccessful logons before a user
                                         is disconnected. (default is 3)

NTLM                   REG_DWORD         0x00: Disables Windows NT
                                         LAN Manager (NTLM)
                                         authentication.

                                         0x01: Attempts NTLM first, and
                                         then uses clear text
                                         authentication.

                                         0x02: Uses NTLM authentication
                                         only.

TelnetPort             REG_DWORD         Defines the Transmission Control
                                         Protocol (TCP) port for Telnet
                                         connections. (default is 23)

TermCap                REG_EXPAND_SZ     Sets the full path to the
                                         "terminal capabilities" file.
                                         This file is similar to a UNIX
                                         file, which is used to define
                                         standard layouts and key mappings
                                         for common emulation types (for
                                         example, VT52, VT100, and ANSI).

NumThreadsPerProcessor REG_EXPAND_SZ     Determines the number of threads
                                         assigned to each processor for
                                         execution. The default value is
                                         set to 10. The minimum value
                                         is 2.

				

NOTE: The NumThreadsPerProcessor value is located in the following registry key:

HKEY_LOCAL_MACHINESoftwareMicrosoftTelnetServer1.0Performance

If you change any of these registry values, you have to stop and then restart the Telnet Server service.

 

When you attempt to connect to a computer that is running Windows XP Professional, you can receive the following error message:

Access Denied: Specified user is not a member of TelnetClients group. Server administrator must add this user to the above group.

Telnet Server has closed the connection.

This behavior can occur because Windows XP, by default, forces all of the incoming network connections (except when they are joined to a domain) to a "guest" level of access. This default behavior ensures that an incoming connection has only guest-level access even if a username and password is specified. NTLM automatically authenticates any network connection that uses the local account credentials as a guest.

To work around this behavior, change the default behavior to enable the local administrator and the members of the TelnetClients group to connect to the network with their proper identities, not as guests:

1. In Control Panel, double-click Administrative Tools.
2. Click Local Security Policy.
3. Locate the policy in the "Security SettingsLocal PoliciesSecurity OptionsNetwork Access: Sharing and security model for local accounts" folder.
4. Right-click the policy, and then click Properties.
5. In the box, click Classic – local users authenticate as themselves.
6. Click OK.

Tlntsvr.exe is located in the %SYSTEMROOT%System32 folder.

When you try to use the Telnet client to connect to a Windows XP 64-Bit Professional computer that is running the Telnet service, you may receive the following error message:

Failure in initializing the telnet session. Shell process may not have been launched.

Telnet Server has closed the connection.

Connection to host lost.

To resolve this problem, follow these steps:

1. At a command prompt on the Windows XP 64-bit Professional host that is running the Telnet service, type cd %systemroot%system32, and then press ENTER.
2. Type net stop tlntsvr, and then press ENTER.
3. Type tlntsvr /unregserver, and then press ENTER.
4. Type tlntsvr /service, and then press ENTER.
5. Type net start tlntsvr, and then press ENTER. Telnet connections to the Telnet service should now be accepted.

Note Do not follow these steps on a Microsoft Windows Server 2003-based domain controller because the tlntsvr /service command to reinstall the service will not work. The command calls the computernameTelnetclient group, but this group does not exist on domain controllers. In Windows Server 2003, you must demote the domain controller to a member server, run the tlntsvr /service command to reinstall the service, and then repromote the server to a domain controller.

 

Resources:

1. Telnet commands
2. Description of the Registry Entries for the Telnet Server Service
3. Error Message: Access Denied; Specified User Is Not a Member of TelnetClients Group
4. Failure in initializing the telnet session. Shell process may not have been launched. Telnet…
5. WinNT Err. Msg: Error 1058: The Specified Service is Disabled and Cannot Be Started