Stop error 0xD1 when you set the SIO_LOOPBACK_FAST_PATH flag in Windows 8 or Windows Server 2012

Aplícase a: Windows Server 2012 DatacenterWindows Server 2012 DatacenterWindows Server 2012 Standard


You have a third-party legacy Transport Driver Interface (TDI) filter driver installed on a computer. If you run code that sets the SIO_LOOPBACK_FAST_PATH flag for a connection, you receive the following Stop error message:


This problem occurs because TDI filter drivers implicitly set the SO_CONDITIONAL_ACCEPT flag for all TCP connections that are opened on that computer. After you set the SIO_LOOPBACK_FAST_PATH option for a loopback connection, a race condition occurs.

TDI filter drivers may be used by some antivirus and VPN software.


To fix this issue, we have released a hotfix for Windows 8 and Windows Server 2012.

Hotfix information

Important If you install a language pack after you install this hotfix, you must reinstall this hotfix. Therefore, we recommend that you install any language packs that you need before you install this hotfix. For more information, see Add language packs to Windows.

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that's described in this article. Apply this hotfix only to systems that are experiencing this specific problem.

If the hotfix is available for download, there's 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 get 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 don't qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, go to the following Microsoft website: Note The "Hotfix Download Available" form displays the languages for which the hotfix is available. If you don't see your language, it's because a hotfix is not available for that language.


There's no prerequisite to apply this hotfix.

Registry information

To use the hotfix in this package, you don't have to make any changes to the registry.

Restart requirement

You may have to restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix doesn't replace a previously released hotfix.


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


See the terminology that Microsoft uses to describe software updates.