Default TCP Window Size Is Still Used After You Specify a Different TCPWindowSize Value (810382)

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

SYMPTOMS

In Windows 2000, when you set the SynAttackProtect registry value to 2, you may not be able to configure the TCP receive window size globally for all interfaces. For example, if you set the SynAttackProtect value in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters key to 2, and then set the TCPWindowSize value in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters key to a value other than the default value, the new window size setting may not apply. The default TCP receive window size is still used.

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 fix is now available from Microsoft, but it is only intended to correct the problem that is described in this article. Apply it only to computers that are experiencing this specific problem. This fix may receive additional testing. Therefore, if you are not severely affected by this problem, Microsoft recommends that you wait for the next Windows 2000 service pack that contains this hotfix.

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

http://support.microsoft.com/contactus/?ws=support

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 typical support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

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
   02-Dec-2002  17:57  5.0.2195.6020     105,232  Msafd.dll
   02-Dec-2002  17:56  5.0.2195.6145     313,648  Tcpip.sys
   31-Jul-2001  00:15  5.0.2195.3988      16,240  Tdi.sys
   02-Dec-2002  17:57  5.0.2195.4874      17,680  Wshtcpip.dll

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, use one of the following methods.

Method 1: Set the SynAttackProtect Registry Value to Either 0 (Zero) or 1

To set the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcip\Parameters\SynAttackProtect value 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.

Method 2: Configure the TCPWindowSize Registry Value at the Interfaces Level

To configure the TCPWindowSize registry value at the interfaces level:

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\Interfaces
On the Edit menu, point to New, and then click DWORD Value.
Type TCPWindowSize, and then press ENTER.
In the right pane, double-click TCPWindowSize.
In the Value data box, type the value that you want, and then click OK.

Note You must use a value that is less than 64240.
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

The TCPWindowSize registry value is used to determine the maximum TCP receive window size that is offered by a computer when it establishes a TCP connection. The receive window specifies the number of bytes that a sender can transmit without receiving an acknowledgment. For additional information about TCP features in Windows 2000, click the following article number to view the article in the Microsoft Knowledge Base:

224829 Description of Windows 2000 TCP Features