Lemonde
  • Lemonde
  • 100% (Exalted)
  • Advanced Member Topic Starter
7 years ago
We are seeing the following after creating a team LAN using the Windows 2016 teaming facility as normal:

Log Name: System
Source: Microsoft-Windows-MsLbfoSysEvtProvider
Date: 10/05/2018 07:53:44
Event ID: 16945
Task Category: None
Level: Warning
Keywords: Classic
User: N/A
Computer: %computername%.domain.suffix
Description:
MAC conflict: A port on the virtual switch has the same MAC as one of the underlying team members on Team Nic Microsoft Network Adapter Multiplexor Driver
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-MsLbfoSysEvtProvider" Guid="{387ed463-8b1b-42c9-9ef0-803fdfd5d94e}" EventSourceName="MsLbfoProvider" />
    <EventID Qualifiers="32768">16945</EventID>
    <Version>0</Version>
    <Level>3</Level>
    <Task>0</Task>
    <Opcode>0</Opcode>
    <Keywords>0x80000000000000</Keywords>
    <TimeCreated SystemTime="2018-05-10T06:53:44.348965900Z" />
    <EventRecordID>715017</EventRecordID>
    <Correlation />
    <Execution ProcessID="4" ThreadID="6276" />
    <Channel>System</Channel>
    <Computer>%computername%.domain.suffix</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="DriverObject">
    </Data>
    <Data Name="Member">Microsoft Network Adapter Multiplexor Driver</Data>
  </EventData>
</Event>
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drdread
  • drdread
  • 100% (Exalted)
  • Advanced Member
5 months ago

The error:


"MAC conflict: A port on the virtual switch has the same MAC as one of the underlying team members on Team NIC Microsoft Network Adapter Multiplexor Driver"


indicates a MAC address duplication issue between a Hyper-V virtual switch and one of the physical adapters in a NIC Team (LBFO Teaming).


Causes:



  1. The Virtual Switch (vSwitch) is attached to a Team NIC, and a MAC address conflict is occurring between the vSwitch port and a physical adapter in the team.

  2. Dynamic MAC assignment is causing a conflict because the vSwitch is using a MAC from a physical NIC.

  3. Incorrect NIC Teaming configuration in Windows Server.

  4. MAC address spoofing issues if manually assigned MACs are conflicting.



Solutions:


1. Verify MAC Addresses & Identify Conflicts


Run the following PowerShell command to check MAC addresses:


Get-NetAdapter | Select-Object Name, MacAddress

If the MAC address of the virtual switch matches any physical NIC in the team, it will cause a conflict.



2. Set Static MAC Address for the Virtual Switch


To prevent conflicts, assign a unique static MAC address to the virtual switch:



  1. Open Hyper-V Manager.

  2. Go to Virtual Switch Manager.

  3. Select the affected virtual switch.

  4. Click on Advanced Features.

  5. Enable MAC Address Spoofing and manually set a unique MAC.


Alternatively, use PowerShell:


Set-VMNetworkAdapter -VMName "YourVMName" -StaticMacAddress "00-15-5D-XX-XX-XX"

(Replace "00-15-5D-XX-XX-XX" with a unique MAC address.)



3. Ensure Correct NIC Teaming Mode


NIC Teaming should not use a team member's MAC. Change the team mode:



  1. Open Server Manager.

  2. Go to Local Server > NIC Teaming.

  3. Select the affected team.

  4. Click Properties.

  5. Change the Load Balancing Mode to Hyper-V Port or Address Hash.


Alternatively, use PowerShell:


Set-NetLbfoTeam -Name "YourTeamName" -LoadBalancingAlgorithm HyperVPort


4. Change the Virtual Switch Connection


If the virtual switch is using a Team NIC, try switching it to Use MAC Address of Management Adapter:


Set-VMSwitch -Name "YourVSwitch" -AllowManagementOS $false

Then, re-enable management if needed:


Set-VMSwitch -Name "YourVSwitch" -AllowManagementOS $true


5. Restart Networking Services


After making changes, restart the networking stack:


Restart-NetAdapter -Name "YourTeamNIC"

Or reboot the system to apply changes.



Summary


✅ Check for MAC conflicts with Get-NetAdapter.
✅ Assign a static MAC to the vSwitch or VM.
✅ Change NIC Teaming mode to avoid conflicts.
✅ Ensure the vSwitch uses a unique MAC and not a team member’s MAC.
✅ Restart network services or reboot if necessary.


Let me know if you need further details! 🚀


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