You are using a Microsoft Windows XP Service Pack 2 (SP2)-based computer or a Microsoft Windows Server 2003 Service Pack 1 (SP1)-based computer that has more than one network adapter. If the Windows Firewall is enabled, you may experience network connection problems on this computer. These connection problems occur even if you have added the following items to the Windows Firewall exception list:

•	The application that tries to make the connection
•	The protocol that is used to make the connection

Additionally, information that resembles the following appears in the Firewall log:Note The information is available only if the Firewall log is enabled in the Windows Security Center. Log information is stored in the %systemroot%\Pfirewall.log file.

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This problem may occur if the following conditions are true:

•	A multi-homed computer receives a network packet on a network adapter (adapter1).
•	The IP destination of the packet is the IP address of another network adapter (adapter2).

In this case, the response to the network packet may be dropped. The anti-spoofing rule examines each send packet to see whether the sending IP address is bound to the adapter1. The answer packet is dropped because the sending IP address is bound to adapter2.

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Windows XP

Hotfix information

A supported hotfix is now 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 service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:Note If additional issues occur or 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. To create a separate service request, visit the following Microsoft Web site:

Prerequisites

There are no prerequisites to install this hotfix.

Restart requirement

You must restart the 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 file attributes) 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 item in Control Panel.
Windows XP Service Pack 2 (SP2)-based versions

File name	File version	File size	Date	Time	Platform
Ipnat.sys	5.1.2600.2831	135,680	21-Jan-2006	01:18	x86

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Windows Server 2003

Service pack information

To resolve this problem, obtain the latest service pack for Windows Server 2003. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

Hotfix information

Prerequisites

To apply this hotfix, you must have Windows Server 2003 Service Pack 1 (SP1) installed on the computer.

Restart requirement

You must restart the 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 file attributes) 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 item in Control Panel.
Windows Server 2003, x86-based versions

File name	File version	File size	Date	Time	Platform
Ipnat.sys	5.2.3790.2745	103,424	12-Jul-2006	10:21	x86

Windows Server 2003, x64-based versions

File name	File version	File size	Date	Time	Platform
Ipnat.sys	5.2.3790.2745	156,160	12-Jul-2006	17:34	x64

Windows Server 2003, Itanium-based versions

File name	File version	File size	Date	Time	Platform
Ipnat.sys	5.2.3790.2745	350,208	12-Jul-2006	17:34	IA-64

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Windows Server 2003 Service Pack 2.

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For more information, click the following article number to view the article in the Microsoft Knowledge Base:

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