DF Bit Is Incorrectly Set to Zero on All Packets Sent From a Windows 2000-Based Computer

Article translations Article translations
Article ID: 332001 - View products that this article applies to.
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This article has been archived.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
Expand all | Collapse all

On This Page

Symptoms

In Windows 2000, when you set the
SynAttackProtect
value 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:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

Cause

This problem occurs because the DF bit option is not initiated correctly when the
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\SynAttackProtect
value is set to 2.

Resolution

Service Pack Information

To 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 Information

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
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

Status

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.

Workaround

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\SynAttackProtect
value to either 0 (zero) or 1:
  1. Click Start, and then click Run.
  2. In the Open box, type regedit, and then click OK.
  3. Locate, and then click the following registry key:
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcip\Parameters
  4. In the right pane, double-click
    SynAttackProtect
    .
  5. In the Value data box, type either 0 or 1, and then click OK.
  6. Quit Registry Editor.

More information

The
SynAttackProtect
registry 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

Properties

Article ID: 332001 - Last Review: October 26, 2013 - Revision: 3.0
Applies to
  • Microsoft Windows 2000 Server
  • Microsoft Windows 2000 Advanced Server
  • Microsoft Windows 2000 Professional Edition
Keywords: 
kbnosurvey kbarchive kbautohotfix kbhotfixserver kbqfe kbnetwork kbwin2ksp4fix kbprb kbbug kbfix kbwin2000presp4fix KB332001

Give Feedback

 

Contact us for more help

Contact us for more help
Connect with Answer Desk for expert help.
Get more support from smallbusiness.support.microsoft.com