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! 🚀