Hyper-V MAC Addresses Duplication or Collison

Networking in Hyper-V is one of the main feature in a virtual infrastructure.

like physical dimension, for each virtual machine ( for each virtual NIC) assigned a MAC address (classic and logic networking).

The question is:

– How these MAC addresses are created ?

– How these MAC addresses are assigned to Virtual machines ?

– How can i avoid MAC addresses collision ?

– Static Mac addresses or Dynamic MAC addresses ?

John Howard -MSFT has written an excellent blog about how MAC addresses are generated and assigned in Hyper-V.


What can we learn from John:

1- MAC addresses are generated based on the Microsoft IEEE Organizationally Unique Identifier 00-15-5D and the last 16 bytes from the Host IP address: MAC address RANGE = 00-15-5D-(Hex(last 16 bytes of Host IP))+00 to 00-15-5D-(Hex(last 16 bytes of Host IP))+ff


If my host IP address is, the last 16 bytes are 20.1, in hex 14-01 and the MAC address range is [00-15-5D-14-01-00;00-15-5D-14-01-ff]

2- How MAC addresses are assigned: Each new created virtual machine NIC receives the next available MAC address.

Example: (NIC1, 00-15-5D-14-01-00), (NIC1, 00-15-5D-14-01-01), (NIC1, 00-15-5D-14-01-02) …

3– If MAC addresses range is saturated: Virtual machine with virtual NIC will be unable to boot

4- Dynamic or Fixed MAC range:

  • In production environment, it’s recommended to fix your MAC      addresses range. This will simplifie management, tracking, avoid collision.
  • If your environment is large, and it’s possible to have two hosts      with the same last 16 bytes, think to fix your MAC addresses range
  • Try to manage your Virtual environment with SCVMM, it automatically      avoid MAC collision, it has global view of all your hosts.

Hyper-V console alternative

Using the Hyper-V console may be sometimes impossible or dificult to realize. The most cases are when you are facing a Windows server 2008 R2 core edition or a Windows Hyper-V server 2008 R2.

Others possibilities are when you are unable to open the Hyper-V console.

Regardless what is your reason, an Hyper-V console alternative exists, and for FREE

5nine Manager for Hyper-V  provides an EASY_Monitoring for Hyper-V and a local Graphical User Interface to Microsoft Hyper-V R2 server. It supports Hyper-V technology on Full and Core installations of Windows Server 2008 R2, as well as on Microsoft Hyper-V Server 2008 R2, which is the Microsoft’s standalone FREE Hypervisor! You can use it when Microsoft SC VMM, or even Hyper-V Manager are not available for Core or Free versions of Server 2008 R2. It also provides Value-Add functions, such as advanced network bindings, performance monitoring, and a hardware profiling for all flavors of Server 2008 and Free/Core Hyper-V installations.

Download 5nine (You must register before downloading it, but for free too )

Hyper-V Remote and Local management troubleshooting

Sometimes, you encounter issues when connecting to Hyper-V console. Problems may occur for different reasons:

– Insufficient permissions

– Firewall exceptions

– Configuration issues

To troubleshoot and resolve this, John Howard -MSFT has written an excellent blog about that.

Hyper-V Remote Management: You do not have the required permission to complete this task. Contact the administrator of the authorization policy for the computer ‘COMPUTERNAME’

– If you want to rapidly configure your Hyper-V remote parameters, see the excellent HVremote script: HVremote