LBFO Dynamic Teaming mode may drop packets in Windows Server 2012 R2

Applies to: Windows Server 2012 R2 DatacenterWindows Server 2012 R2 StandardWindows Server 2012 R2 Essentials

This article describes an issue that occurs when you use load balancing and failover (LBFO) Dynamic Teaming in Windows Server 2012 R2. You can fix this issue by using the update in this article. Before you install this update, see the Prerequisites section.


Windows Server 2012 R2 server may drop packets if the following settings are configured:
  • Network Interface Card (NIC) Teaming is enabled.
  • Teaming Load Balancing Mode: Dynamic.
  • More than one NIC is in Active Mode.
When packet dropping occurs, event ID 8 is logged in Event Viewer under Applications and Services Logs > Microsoft > MsLbfoProvider > Operational view that looks something like this: Therefore, you may encounter the following issues but not limit to these issues:
  • Cluster nodes are unexpectedly removed from cluster groups.
  • SQL database transaction failures.
  • TCP connection stops.


This issue occurs because a race condition causes NIC Teaming Dynamic load balance algorithm to drop packets.

How to get this update

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

Method 1: Windows Update

This update is provided as a Recommended update on Windows Update. For more information on how to run Windows Update, see How to get an update through Windows Update.

Method 2: Microsoft Download Center

The update is available for download from the Microsoft Download Center:

Download Download the Windows Server 2012 R2 package now.

For more information about how to download Microsoft support files, click the following article number to view the article in the Microsoft Knowledge Base:
119591 How to obtain Microsoft support files from online services
Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help prevent any unauthorized changes to the file.

Update detail information


To apply this update, you must have April 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 (2919355) installed in Windows Server 2012 R2.

Registry information

To apply this update, you don't have to make any changes to the registry.

Restart requirement

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

Update replacement information

This update doesn't replace a previously released update.


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

More Information

Dynamic teaming load balancing is a new feature in Windows Server 2012 R2. Windows Server 2012 R2 servers default to dynamic mode when teaming NICs are created on physical computers. LBFO driver versions earlier than this KB 3137691 may incorrectly drop packets. Such packet loss can increase as processor cores are added and network traffic increases.


Learn about the terminology that Microsoft uses to describe software updates.

File Information

The English (United States) version of this software update installs files that have the attributes that are listed in the following tables.