MAC Address Management with MED-V V2 Workspaces

  • Article

In general, it is recommended to leverage the Virtual PC NAT mode (shared networking) when implementing MED-V workspaces. This will take care of any IP address and MAC address management issues. There may be reasons, however, for you to leverage bridged mode in place of NAT mode.

Bear in mind, when you choose bridged mode, the host network adapter enters into promiscuous mode and the MAC and IP address of the VPC will appear to the external network. To all network entities outside the host, the VPC appears as a separate entity different from the host. In this mode, the network service redirects all incoming and outgoing network traffic. Traffic is filtered based on the MAC addresses and routed to the correct VPC.

MED-V workspaces configured to use host network adapter networking setting can communicate with other virtual machines that are configured to use the same host network adapter, with the host computer, and with all computers on the external network.

Since MED-V is delivering a stand-alone single image that will be sysprepped possibly to multiple users, Virtual PC has to avoid deploying the virtual machine with the same MAC address to many users. It has to be assured that each virtual machine will get a new MAC address the first time it starts.

The VMCX will have the value changed:

<ethernet_card_address type="bytes">0003FFXXXXXX</ethernet_card_address>

to this

<ethernet_card_address type="bytes"></ethernet_card_address>

Virtual PC will then create a new address for the VPC during MED-V's FTS.

Post-Deployment MAC Address Management

In some cases, you may desire the MED-V workspaces maintain a fixed MAC address due to DHCP IP address management or other netowrk-related policies.

Ensuring the VMCX file maintains a static address will have to happen post deployment (POST FTS.) You will need to modify the VMCX file to have it at the desired static MAC address you want. The locations will vary depending on whether the workspace is multi-user or not.

  • Shared Workspace - Even though the VHD is stored here - C:\ProgramData\Microsoft\Medv\AllUsers\Virtual Machines, there will still be a per-user registered VMCX file in the user's profile (C:\Users\<USERNAME>\Virtual Machines\<VPCNAME>.VMCX. This is only the registration as the XML you would modify with the static image would be in %LOCALAPPDATA%\Microsoft\MEDV\v2\Virtual Machines\<VPCNAME>.vmc
  • Per-User Workspaces - C:\Users\<Username>\AppData\Local\Microsoft\MEDV\v2

Please note the MED-V Workspace’s MAC address will also change under these conditions:

  • When a MAC address conflict is detected with another running virtual machine.
  • When the virtual machine is registered - In the case of MED-V could be after any reset, additional user logs on and triggers FTS. The purpose of this is so that if a user takes an existing virtual machine and copies it - they can then bring it up without having to worry about duplicate MAC addresses. 
  • When the workspace is reset in MED-V. This re-triggers FTS