Failover Cluster Validation Firewall Error in Windows Server 2008 R2

An issue involving a firewall configuration error in the cluster validation process just surfaced here in Microsoft Support so I thought I would post a quick blog in an effort to not only inform our readership, but to ‘nip this in the bud’ before we start seeing more. 

                After running a Windows Server 2008 R2 Failover Cluster validation report, you may see the following error –

“An error occurred while executing the test.  There was an error verifying the firewall configuration.  An item with the same key has already been added”

The error, as is, does not provide a clear direction to take when trying to troubleshoot.  Thanks to the efforts of Cluster Product Group, the source of the issue was identified and a quick data collection process can be executed to help determine the ‘root’ cause.

The firewall configuration error is reported if any of the network adapters across the cluster nodes being validated have the same Globally Unique Identified (GUID).  This can be determined by running the following WMI query on each node in the cluster and comparing the results.  I chose to run the query inside PowerShell  to display sample data in a formatted list-

GetWMI Win32_NetworkAdapter | fl Name,GUID


The sample output above shows the information associated with the three physical network adapters that exist in one of the nodes in my cluster.  After the data is gathered from each node in the cluster, you just need to compare it and identify the duplicate GUID information.

The next logical question is, “How does one find themselves in this predicament?”  In the cases we have encountered thus far, the cluster nodes were being deployed in an unsupported manner.  In each case an ‘image’ was being used to deploy the nodes.  We discovered that the operating system image was not properly prepared before being deployed by, for example, running sysprep.

Hopefully this information will be useful and will help avoid further occurrences of this issue.  Thanks again and please come back.

Additional References:

Failover Cluster Step-by-Step Guide: Validating hardware for a Failover Cluster

KB 943984:  The Microsoft Policy for Windows Server 2008 Failover Clusters

Deployment Tools Technical Reference

Chuck Timon
Senior Support Escalation Engineer
Microsoft Enterprise Platforms Support