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Consider the following scenario. You have installed the MS05-019 security update on a Microsoft Windows XP Service Pack 2 (SP2)-based client computer. Microsoft Windows Firewall is enabled on the client computer. When you try to send data packets from the client computer to a server, you do not receive Internet Control Message Protocol (ICMP) "Destination Unreachable" messages when the data packets are larger than the Maximum Transfer Unit (MTU) size limit that is set on the server.
This problem may occur when either of the following conditions is true:
The client computer is using a dial-up connection or a virtual private network (VPN) connection.
The client computer is using an FTP server to transfer data.
For more information about the MS05-019 security update, click the following article number to view the article in the Microsoft Knowledge Base:
893066 MS05-019: Vulnerabilities in TCP/IP could allow remote code execution and denial of service
This problem occurs because the Network Address Translation (NAT) driver that Windows Firewall uses does not translate the ICMP data correctly on the client computer.
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:
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.
To install this hotfix, you must be running Windows XP Professional SP2.
You must restart your computer after you apply this hotfix.
Hotfix replacement information
This hotfix does not replace any other hotfixes.
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.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
For more information, 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
For more information about Internet Control Message Protocol, click the following article number to view the article in the Microsoft Knowledge Base:
170292 Internet Control Message Protocol (ICMP) basics
For more information about default Maximum Transfer Unit sizes, click the following article number to view the article in the Microsoft Knowledge Base:
314496 Default MTU size for different network topology