You cannot use Verizon FiOS products at their full speed on a Windows Vista-based computer

Problem description

On a computer that is running Windows Vista, you try to use the Verizon speed optimizer tool to optimize network performance. When you do this, you may notice that the Windows Vista-based computer does not achieve the Internet connection speed improvement that is achieved in Windows XP. Therefore, you cannot use Verizon FiOS products at their full speed.

Probable cause

This problem occurs because of the TCP/IP protocol stack changes that were made in Windows Vista. On a Windows Vista-based computer, the TCP/IP protocol stack changes do not allow registry key changes in some areas. Additionally, in the source code, the TCPAutoTuning feature is set to "off." These changes cause the problem that is mentioned in the "Problem description" section.


Service pack information

To resolve this problem, obtain the latest service pack for Windows Vista. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
935791 How to obtain the latest Windows Vista 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. 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.


There are no prerequisites for installing this hotfix.

Restart requirement

You do not have to restart the computer after you apply this hotfix. However, you must restart the computer after you set the TcpAutoTuning value in the registry, as described in the "How to enable the hotfix" section.

Hotfix replacement information

This hotfix does not replace a previously released hotfix.

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 Vista, 32-bit versions
File nameFile versionFile sizeDateTimePlatform
Update.mumNot applicable2,00221-Jul-200712:26Not applicable
X86_2d1491e2ae43efd26100d561613492f5_31bf3856ad364e35_5.1.6000.20645_none_2736f6926c773ef7.manifestNot applicable69521-Jul-200712:26Not applicable applicable41,45121-Jul-200712:26Not applicable
Windows Vista, 64-bit versions
File nameFile versionFile sizeDateTimePlatform
Amd64_75e3d8c57636d929b14b0fd81e564298_31bf3856ad364e35_5.1.6000.20645_none_5a47331b95817f45.manifestNot applicable69921-Jul-200712:26Not applicable
Amd64_a4e35a0d49d382441a36095e8e8f362a_31bf3856ad364e35_5.1.6000.20645_none_232aa5bf7a8f5cf6.manifestNot applicable69921-Jul-200712:26Not applicable applicable41,48121-Jul-200712:38Not applicable
Package_1_for_kb939006~31bf3856ad364e35~amd64~~ applicable1,79621-Jul-200712:26Not applicable
Package_2_for_kb939006~31bf3856ad364e35~amd64~~ applicable2,01321-Jul-200712:26Not applicable
Update.mumNot applicable1,92521-Jul-200712:26Not applicable applicable34,82821-Jul-200712:38Not applicable

How to enable the hotfix

To have us fix this problem for you, go to the “Fix it for me” section. If you’d rather fix this problem yourself, go to the “Let me fix it myself” section.

Fix it for me
To fix this problem automatically, click the
Fix this problemlink. Then click
Runin the
File Downloaddialog box, and follow the steps in this wizard.

NoteThis wizard is temporarily in English only. However, the automatic fix also works for other language versions of Windows.

NoteIf you are not on the computer that has the problem, you can save the automatic fix to a flash drive or a CD so that you can run it on the computer that has the problem.

Now go to the "Did this fix the problem?" section.
Let me fix it myself

To use one of the hotfixes in this package, you must either create a registry key or modify a registry key.To do this, follow these steps.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base:
322756 How to back up and restore the registry in Windows
  1. Click Start, click Run, type regedit, and then click OK.
  2. Locate and then click the following registry subkey:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Internet Settings\WinHttp
  3. On the Edit menu, point to
    New, and then click DWORD Value.
  4. In the details pane, type
    TcpAutoTuning, and then press ENTER.
  5. Right-click TcpAutoTuning, and then click
  6. In the Edit DWORD Value dialog box, click
    Decimal under Base.
  7. In the Value data box, type
    1, and then click OK.
  8. Exit Registry Editor.
  9. Restart the computer.


Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section. This problem was first corrected in Windows Vista Service Pack 1.

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

Did this fix the problem?

Check whether the problem is fixed. If the problem is fixed, you are finished with this article. If the problem is not fixed, you can contact support.

ID articolo: 939006 - Ultima revisione: 09 ott 2011 - Revisione: 1