The TCP receive window size cannot be changed by configuring the registry on the passive open side when a TCP/IPv6 connection is used on a Windows Server 2003-based computer

On a Windows Server 2003-based computer, the TcpWindowSize registry entry does not work on the passive open side for TCP/IPv6 connections.

For example, the TcpWindowSize registry entry has the value 65535 on both the active open side and the passive open side. However, after the TCP/IPv6 connection is established, the actual TCP receive window size is 16384 instead of 65535.

Additional investigation indicates that the passive open side uses the 16384 value as the preferred receive window size even though the registry key is configured as 65535.

Notes

• This problem occurs only on the TCP/IPv6 passive open side.
• This problem occurs only for TCP/IPv6 connections. TCP/IPv4 connections do not have this problem.
• You configure the TcpWindowSize registry entry in the following location:
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\TcpWindowSize

This problem occurs because the Tcpip6.sys driver ignores the value of the TcpWindowSize registry entry on the passive open side. Instead, the driver uses a default value of 16384.

To resolve this problem, apply the following hotfix. After you apply this hotfix, the system reads the TcpWindowSize registry entry on the passive open side, and it uses this value to establish TCP/IPv6 connections.

Note The system reads the TcpWindowSize registry entry in the following location:

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 the problem described in this article. 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.

Prerequisites

To apply this hotfix, you must have Windows Server 2003 Service Pack 2 (SP2) installed.

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

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 with Service Pack 2, x86-based versions

Windows Server 2003 with Service Pack 2, Itanium-based versions

Windows Server 2003 with Service Pack 2, x64-based versions

Windows XP x64-based versions with Service Pack 2

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

There are two sides to a TCP connection (the active open side and the passive open side). The active open side initiates the transmission, and the passive open side waits for a transmission.

In the TCP/IPv6 protocol, the receive window size can be configured in both of the following locations:After you apply this hotfix, you can update the value of the TcpWindowSize registry entry in the first location.