DF Bit Is Incorrectly Set to Zero on All Packets Sent From a Windows 2000-Based Computer
This article was previously published under Q332001
This article has been archived. It is offered "as is" and will no longer be updated.
IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:
256986 Description of the Microsoft Windows Registry
In Windows 2000, when you set the
SynAttackProtectvalue in the following registry key to 2, the "don't fragment" or DF bit is incorrectly set to 0 on all packets that are sent from the computer:
This problem occurs because the DF bit option is not initiated correctly when the
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\SynAttackProtectvalue is set to 2.
Service Pack InformationTo resolve this problem, obtain the latest service pack for Microsoft Windows 2000. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:
260910 How to Obtain the Latest Windows 2000 Service Pack
Hotfix InformationA 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: 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 Global 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-Nov-2002 16:36 5.0.2195.6127 118,896 Afd.sys 22-Nov-2002 22:29 5.0.2195.6020 105,232 Msafd.dll 22-Nov-2002 22:28 5.0.2195.6139 313,648 Tcpip.sys 31-Jul-2001 00:15 5.0.2195.3988 16,240 Tdi.sys 22-Nov-2002 22:29 5.0.2195.4874 17,680 Wshtcpip.dll
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was first corrected in Microsoft Windows 2000 Service Pack 4.
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. To work around this problem, set the
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcip\Parameters\SynAttackProtectvalue to either 0 (zero) or 1:
- Click Start, and then click Run.
- In the Open box, type regedit, and then click OK.
- Locate, and then click the following registry key:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcip\Parameters
- In the right pane, double-click SynAttackProtect.
- In the Value data box, type either 0 or 1, and then click OK.
- Quit Registry Editor.
SynAttackProtectregistry value is used to harden the TCP/IP stack against denial of service attacks. You configure this value according to the level of protection that you want to set. For additional information about TCP/IP-related registry values that you can configure to harden the TCP/IP stack on computers that are directly connected to the Internet, click the following article number to view the article in the Microsoft Knowledge Base:
315669 HOW TO: Harden the TCP/IP Stack Against Denial of Service Attacks in Windows 2000
Article ID: 332001 - Last Review: 10/26/2013 08:19:00 - Revision: 3.0
Microsoft Windows 2000 Server, Microsoft Windows 2000 Advanced Server, Microsoft Windows 2000 Professional Edition
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