25 July 2011

Setting MAC Address for VM NICs using PowerShell

A bit ago, there were some questions in the VMware VMTN community forums about setting explicit MAC addresses for VMs' NICs.

While this can be done via PowerCLI using the Set-NetworkAdapter cmdlet, the MAC address range is restricted to 00:50:56:00:00:00 - 00:50:56:3F:FF:FF when using the cmdlet, which is only a subset of the range that VMware uses.

An example came up where one might need to set the MAC address to something in a valid VMware range (with VMware OUIs like "00:50:56" or "00:0C:29") outside of the subset above. This can be done using the Web Services API, as it does not have the same range limitation as the cmdlet. The well-commented code below shows how to do so using the API:

## script function:  set the MAC address of a VM's NIC
## Author: vNugglets.com

## the name of the VM whose NIC's MAC address to change
$strTargetVMName = "myVM01"
## the MAC address to use
$strNewMACAddr = "00:50:56:90:00:01"

## get the .NET view object of the VM
$viewTargetVM = Get-View -ViewType VirtualMachine -Property Name,Config.Hardware.Device -Filter @{"Name" = "^${strTargetVMName}$"}
## get the NIC device (further operations assume that this VM has only one NIC)
$deviceNIC = $viewTargetVM.Config.Hardware.Device | Where-Object {$_ -is [VMware.Vim.VirtualEthernetCard]}
## set the MAC address to the specified value
$deviceNIC.MacAddress = $strNewMACAddr
## set the MAC address type to manual
$deviceNIC.addressType = "Manual"

## create the new VMConfigSpec
$specNewVMConfig = New-Object VMware.Vim.VirtualMachineConfigSpec -Property @{
   ## setup the deviceChange object
   deviceChange = New-Object VMware.Vim.VirtualDeviceConfigSpec -Property @{
       ## the kind of operation, from the given enumeration
       operation = "edit"
       ## the device to change, with the desired settings
       device = $deviceNIC
   } ## end New-Object
} ## end New-Object

## reconfigure the "clone" VM

The ReconfigVM() method does not care if the new MAC address is a valid VMware MAC address. It does not even seem to care if the new MAC address string is a valid hex MAC address. So, use with care -- one would not want to break networking on their precious VM by setting its NIC to have an invalid MAC address, or a duplicate, etc.

Other info: the valid VMware OUIs can be found many places, like at the IEEE.org Public Listing search site.

Update 25 Nov 2011:
Do note that changing the MAC address of a VM NIC to something outside of the "accepted" range will cause other PowerCLI cmdlets and the vSphere client to report that the NIC's MAC is "not in the valid range", and may prevent further operations on that VM's NIC with those tools.  Thank-you to the anonymous commenter here and to LucD (in the VMware Communities thread at http://communities.vmware.com/message/1869800#1869800) for highlighting this point.

Update 31 Dec 2011:
The -Filter parameter for the Get-View call on line 10 was using a regular expression that had the possibility of returning more than one VM View object.  I have updated the regular expression to only match VMs of exactly the given name.  Thanks go to Joep Piscaer for pointing out the issue.  The code in this post has been updated.