On a computer that is running Microsoft Windows XP with Service Pack 2 (SP2), programs that connect to IP addresses that are in the loopback address range may not work as you expect. For example, you may receive an error message that says that you cannot establish a connection.

CAUSE

This problem occurs if the program connects to a loopback address other than 127.0.0.1. Windows XP Service Pack 2 (SP2) prevents connections to all IP addresses that are in the loopback address range except for 127.0.0.1.

RESOLUTION

Hotfix information

A supported hotfix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Only apply it to systems that are experiencing this specific problem. This hotfix may receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Windows XP service pack that contains this hotfix.

To resolve this problem immediately, contact Microsoft Product Support Services to obtain the hotfix. For a complete list of Microsoft Product Support Services phone numbers and information about support costs, visit the following Microsoft Web site:

Note In special cases, charges that are ordinarily incurred for support calls may be canceled if a Microsoft Support Professional determines that a specific update will resolve your problem. The usual support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

Prerequisites

This hotfix requires Windows XP Service Pack 2 (SP2).

Restart requirement

You have to restart your computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix 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-Aug-2004  22:50  5.1.2600.2505  359,040  Tcpip.sys

STATUS

MORE INFORMATION

For additional information about how to troubleshoot a problem where Remote Desktop Connection does not permit loopback connections to ports that it is not listening on, click the following article number to view the article in the Microsoft Knowledge Base:

817293 Remote Desktop Connection does not permit loopback connections to ports that it is not listening on

For additional information about troubleshooting TCP/IP connectivity issues with Windows XP, click the following article number to view the article in the Microsoft Knowledge Base:

For additional information about standard terminology that is used to describe Microsoft software updates, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

The information in this article applies to:

Microsoft Windows XP Professional Service Pack 2 (SP2)
Microsoft Windows XP Home Edition Service Pack 2 (SP2)
Microsoft Windows XP Media Center Edition Service Pack 2 (SP2)
Microsoft Windows XP Tablet PC Edition 2005

Last Reviewed:	8/16/2004 (1.0)
Keywords:	kbQFE kb3rdparty kbprint kbnetwork kbfix kbbug KB884020 kbAudITPRO kbAudEndUser

A. M. Software Services, Inc. - Knowledge Base

Programs that connect to IP addresses that are in the loopback address range may not work as you expect in Windows XP Service Pack 2

SYMPTOMS