A port on the virtual switch has the same MAC as one of the underlying team members on Team Nic Event ID 16945 #winserv

If you are using Windows Server 2012 R2 and configured NIC Teaming you could have this Event ID : 16945

This is showing up as a Warning in the event log.
What the event is saying is that you have a host vNIC (virtual NIC presented to the host that is connected to the Virtual Switch)
That has the same MAC address as one of the NIC (physical NIC) members of the NIC team.  
This shouldn’t cause an issue as long as the team member that has the same MAC as the vNIC remains in the team. If that team member is ever removed from the team and attempt standalone operation with that MAC then there could be duplicate MAC address on the network assuming the vNIC is also in operation.  


What is NIC Teaming?

A solution commonly employed to solve the network availability and performance challenges is NIC Teaming. NIC Teaming (aka NIC bonding, network adapter teaming, Load balancing and failover, etc.) is the ability to operate multiple NICs as a single interface from the perspective of the system. In Windows Server 2012, NIC Teaming provides two key capabilities:

  1. Protection against NIC failures by automatically moving the traffic to remaining operational members of the team, i.e., Failover, and
  2. Increased throughput by combining the bandwidth of the team members as though they were a single larger bandwidth interface, i.e., bandwidth aggregation.

My current Team


You can see a all the vNIC/pNIC and MAC addresses by doing a “get-netadapter | sort macaddress” in PowerShell. 
You should see one of your physical NIC and a virtual NIC called something like "vEthernet" and both will have the same MAC. 

get-netadapter | sort macaddress


But what If I change the MAC of the Team by looking at the properties of the team interface (in Network Connections, "Microsoft Network Adapter Multiplexor", then click the Configure button, then select the Advanced tab.
The 7th item in the list is MAC Address. You could configure a MAC there for the team.



The Team is has now the given MAC More about the MAC reservations

Hyper-V How To: Manage MAC Address Conflicts


Windows Server 2012 NIC Teaming (LBFO) Deployment and Management


Author: Robert Smit [MVP]

Robert Smit is Senior Technical Evangelist and is a current Microsoft MVP in Clustering as of 2009. Robert has over 20 years experience in IT with experience in the educational, health-care and finance industries. Robert’s past IT experience in the trenches of IT gives him the knowledge and insight that allows him to communicate effectively with IT professionals who are trying to address real concerns around business continuity, disaster recovery and regulatory compliance issues. Robert holds the following certifications: MCT - Microsoft Certified Trainer, MCTS - Windows Server Virtualization, MCSE, MCSA and MCPS. He is an active participant in the Microsoft newsgroup community and is currently focused on Hyper-V, Failover Clustering, SQL Server, Azure and all things related to Cloud Computing and Infrastructure Optimalization. Follow Robert on Twitter @ClusterMVP Or follow his blog https://robertsmit.wordpress.com Linkedin Profile Http://nl.linkedin.com/in/robertsmit Robert is also capable of transferring his knowledge to others which is a rare feature in the field of IT. He makes a point of not only solving issues but also of giving on the job training of his colleagues. A customer says " Robert has been a big influence on our technical staff and I have to come to know him as a brilliant specialist concerning Microsoft Products. He was Capable with his in-depth knowledge of Microsoft products to troubleshoot problems and develop our infrastructure to a higher level. I would certainly hire him again in the future. " Details of the Recommendation: "I have been coordinating with Robert implementing a very complex system. Although he was primarily a Microsoft infrastructure specialist; he was able to understand and debug .Net based complext Windows applications and websites. His input to improve performance of applications proved very helpful for the success of our project

7 thoughts on “A port on the virtual switch has the same MAC as one of the underlying team members on Team Nic Event ID 16945 #winserv”

  1. How do I do this on a server running core? I have been trying to figure this out for a while now.

  2. that is a great question with netsh you can do this or change this in the register like this
    You need to change a registry key like so
    reg add HKLM SYSTEM\CurrentControlSet\Control\Class\{4D36E972-E325-11CE-BFC1-08002BE10318}001] /v NetworkAddress /d 0123456789AB
    Replace 0001 with your interface number and 0123456789AB with desired network address.
    Next, disable and enable the network card
    Subsitute the actual network connection name if it isn’t Local Area Connection.
    netsh interface set interface “Local Area Connection” DISABLED
    netsh interface set interface “Local Area Connection” ENABLED

    more info : https://technet.microsoft.com/en-us/library/cc732869(v=ws.10).aspx

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.

%d bloggers like this: