This article describes a problem in which Network Load Balancing (NLB) cluster communication gets interrupted randomly in Windows Server 2012 R2. An update is available to fix this problem. Before you install this update, see the Prerequisites section.
This problem occurs when a security feature is enabled in your environment to prevent MAC impersonation and when an NLB cluster is set to operate in Internet Group Management Protocol (IGMP) multicast mode. In this configuration, the IGMPv1 multicast membership reports are randomly sent by having an incorrect source MAC address. This situation interferes with the security settings of the intermediate devices that are used, and this breaks the cluster communication.
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.
For more information about how to download Microsoft support files, select 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.
To apply this update, you don't have to make any changes to the registry.
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.
Learn about the terminology that Microsoft uses to describe software updates.
The English (United States) version of this software update installs files that have the attributes that are listed in the following tables. The dates and times for these files are listed in Coordinated Universal Time (UTC). Be aware that dates and times for these files on your local computer are displayed in your local time and with your current daylight saving time bias. The dates and times may also change when you perform certain operations on the files.
Windows Server 2012 R2
The files that apply to a specific product, milestone (RTM, SPn), and service branch (LDR, GDR) can be identified by examining the file version numbers as shown in the following table.
Windows Server 2012 R2
GDR service branches contain only those fixes that are widely released to address widespread, critical issues. LDR service branches contain hotfixes in addition to widely released fixes.
The MANIFEST files (.manifest) and the MUM files (.mum) that are installed for each environment are listed in the "Additional file information" section. MUM, MANIFEST, and the associated security catalog (.cat) files, are very important to maintain the state of the updated components. The security catalog files, for which the attributes are not listed, are signed with a Microsoft digital signature.