Article ID: 817892 - Last Review: December 3, 2007 - Revision: 6.11

Cannot Connect to a Windows-Based Server That Is Running NAT If the Client Source Port Is 1723

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SUMMARY

If Network Address Translation (NAT) is in use on a server that is running Windows Server 2003 or Windows 2000, connections cannot be made to the server's external interface if the source port of a client computer is port 1723.

You can enable NAT by turning on Internet Connection Sharing or by using Microsoft Internet Security and Acceleration (ISA) Server 2000.
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CAUSE

Ipnat.sys does not allow a port that is already associated with the Point-to-Point Tunneling Protocol (PPTP) to be used.
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RESOLUTION

Windows Server 2003

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:
http://support.microsoft.com/contactus/?ws=support (http://support.microsoft.com/contactus/?ws=support)
Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel. 
   Date         Time   Version       Size    File name
   ----------------------------------------------------
   02-Dec-2003  17:50  5.2.3790.107  80,384  Ipnat.sys
Note As part of the resolution, you must add the following registry entry to the
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\IpNat\Parameters
subkey.

Warning If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.
Data type:
DWORD

Entry name:
DisablePPTPEditor

Value data:
1
(to disable PPTP Editor) or
0
(to enable PPTP Editor)
Set this value to
1
if you are experiencing the problem that is described in this article.
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Windows 2000

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, submit a request to Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site:
http://support.microsoft.com/contactus/?ws=support (http://support.microsoft.com/contactus/?ws=support)
Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

The English version of this fix has the file attributes (or later) that are listed in the following table. The dates and times for these files are listed in coordinated universal time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time tool in Control Panel. 
   Date         Time   Version        Size    File name
   ----------------------------------------------------
   13-May-2003  12:50  5.0.2195.6745  67,184  Ipnat.sys
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STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.
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APPLIES TO
  • Microsoft Windows Server 2003, Standard Edition (32-bit x86)
  • Microsoft Windows XP 64-Bit Edition Version 2003
  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows Small Business Server 2003 Premium Edition
  • Microsoft Windows Small Business Server 2003 Standard Edition
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Keywords: 
kbautohotfix kbhotfixserver kbqfe kbwinserv2003presp1fix kbwin2000presp5fix kbfix kbbug KB817892
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