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Microsoft KB Archive/170998

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Knowledge Base

Cannot Log in to Windows NT Domain Over Internet Connection

Article ID: 170998

Article Last Modified on 1/20/2007


  • Microsoft Windows 95
  • Microsoft Windows 98 Standard Edition
  • Microsoft Windows NT Server 3.51
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 3.5
  • Microsoft Windows NT Workstation 3.51
  • Microsoft Windows NT Workstation 4.0 Developer Edition

This article was previously published under Q170998


If you are connected to the Internet through an Internet service provider (ISP), you may not be able to log in to a Windows NT Domain, or use Microsoft Networking functionality to connect to another Windows NT-based or Windows 95/98-based computer on the Internet. This may occur even though you may have been able to in the past.


A number of ISPs have disabled User Datagram Protocol (UDP) ports 137 and 138 and Transmission Control Protocol (TCP) port 139 on their routers to reduce network traffic and provide protection against out-of-band (OOB) data attacks on servers. Microsoft Networking components rely on these ports (especially TCP port 139) for NetBIOS communication.

If you could previously use Microsoft Networking components over the Internet but no longer can, contact your ISP to determine if UDP ports 137 or 138 or TCP port 139 has been disabled on the ISP's routers.

NOTE: This method of connecting to a Windows NT domain over the Internet is not a secure configuration and is not recommended by Microsoft. However, you can use the Point-to-Point Tunneling Protocol (PPTP) as an alternative method for communicating with your network over the Internet. PPTP is a networking technology that supports multiprotocol virtual private networks (VPNs), enabling remote users to access corporate networks securely across the Internet. Using PPTP, remote users can use Windows NT Workstation, Windows 95/98, and other point-to-point protocol (PPP)-enabled computers to dial into a local Internet service provider to connect securely to their corporate networks using the Internet.


For more information about TCP ports, see the following RFC:

RFC-1700: Internet Assigned Numbers

For additional information about PPTP, see the following articles in the Microsoft Knowledge Base:

161410 How to Set Up a Private Network Over the Internet Using PPTP

154062 How to Set Up a Windows NT PPTP Client

For additional information about problems connecting to computers running Microsoft Networking components over the Internet, see the following article in the Microsoft Knowledge Base:

142027 Troubleshooting NET USE Failure (When PING NetBIOS Name Works)

For additional information about out-of-band data, see the following articles in the Microsoft Knowledge Base:

143478 Stop 0A in TCPIP.SYS When Receiving Out Of Band (OOB) Data

168747 Update to Windows 95 TCP/IP to Address Out-of-Band Issue

For information about the types of network traffic created when you are using Microsoft Networking components (without PPTP), see the following article in the Microsoft Knowledge Base:

139608 SMB Traffic During Windows NT Domain Logon

Additional query words: winnt

Keywords: kbinfo kbnetwork KB170998