Hotfix enables the configuration of the TCP maximum SYN retransmission amount in Windows 7 or Windows Server 2008 R2

Windows Server 2008 R2 EnterpriseWindows Server 2008 R2 DatacenterWindows Server 2008 R2 for Itanium-Based Systems

Introduction


This article introduces a hotfix that re-enables the configuration of the number of TCP maximum SYN retransmissions on a computer that is running Windows 7 or Windows Server 2008 R2. After you install the hotfix, the following actions are possible:
  • You can configure the TCP maximum SYN retransmission value by running the following netsh command as administrator:
    netsh interface tcp set global MaxSynRetransmissions=number
    Notes
    • The minimum SYN retransmission value is 2, and the maximum value is 8.
    • You do not have to restart the computer after you run the command.
  • You can query the TCP maximum SYN retransmission value by running the netsh interface tcp show global command. The result resembles the following:
    TCP Global Parameters
    Receive-Side Scaling Stateenabled
    Chimney Offload Stateautomatic
    NetDMA Stateenabled
    Direct Cache Acess (DCA)disabled
    Receive Window Auto-Tuning Levelnormal
    Add-On Congestion Control Providernone
    ECN Capabilitydisabled
    Max SYN Retransmissions2
Note In Windows 7 and Windows Server 2008 R2, the TCP maximum SYN retransmission value is set to 2, and is not configurable. Because of the 3-second limit of the initial time-out value, the TCP three-way handshake is limited to a 21-second timeframe (3 seconds + 2*3 seconds + 4*3 seconds = 21 seconds).

MORE INFORMATION


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 website: 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 be running one of the following operating systems:
  • Windows 7
  • Windows 7 Service Pack 1 (SP1)
  • Windows Server 2008 R2
  • Windows Server 2008 R2 Service Pack 1 (SP1)
For more information about how to obtain a Windows 7 or Windows Server 2008 R2 service pack, click the following article number to view the article in the Microsoft Knowledge Base:

976932 Information about Service Pack 1 for Windows 7 and for Windows Server 2008 R2

Registry information

To apply this hotfix, you do not have to make any changes to the registry.

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

Status


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

More Information


On a computer that is running a Windows operating system earlier than Windows Vista or Windows Server 2008, you can configure the TCP maximum SYN retransmission value by changing the TcpMaxConnectRetransmissions registry entry that is located under the following registry subkey:
\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters
Note The TcpMaxConnectRetransmissions registry entry is not available in Windows Vista, Windows Server 2008, Windows 7 , Windows Server 2008 R2, or any later version of Windows.

For more information about the TcpMaxConnectRetransmissions registry entry, go to the following Microsoft website:For more information about the initial TCP time-out value, click the following article number to view the article in the Microsoft Knowledge Base:
2472264 You cannot customize some TCP configurations by using the netsh command in Windows Server 2008 R2
For more information about software update terminology, 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