• This article applies only to ESXi/ESX 4.0 and ESXi 5.1 Patch 2 only.
• The ESXi 5.1 GA does not have this functionality. The ESXi 5.1 host must include the patch VMware ESXi 5.1, Patch ESXi510-201307401-BG: Updates esx-base and misc-drivers (2052144).
• For information related to ESX/ESXi 4.1 and ESXi 5.0, see the Mac Addresses section in the vSphere Networking Guide for your version of ESX/ESXi.

• You cannot change the MAC address of a network card from within a virtual machine.
• The options to change the NetworkAddress or Locally Administered Address parameters on the network adapters in the virtual machine are not available. For more information, see Changing a MAC address in a Windows virtual machine (1008473).
• Attempting to changing the MAC address manually from the vSphere Client fails with the error:
  
  The MAC address entered is not in the valid range. Valid values are between xx:xx:xx:xx:xx
   
• Changing the MAC address in the virtual machine .vmx configuration file fails with the error:
  
  Please specify a static Ethernet address for ethernet0. Failed to configure ethernet0

Add or change MAC address information to the .vmx file on the ESX/ESXi host

1. Shut down the virtual machine.
2. Right-click the virtual machine and click Remove from Inventory.
3. Login as the root user to a console session on the ESX/ESXi host. For more information, see Tech Support Mode for Emergency Support (1003677).
4. Go to the virtual machine home directory:
   
   # cd /vmfs/volumes/DatastoreName/VMFolderName
    
5. Make a backup of the existing virtual machine's .vmx configuration file with the command:
   
   # cp vmname.vmx vmname.vmx.old
    
6. Open the .vmx configuration file in an editor such as vi or nano and add or change the following entries:
   
   ethernetN.checkMACAddress = “FALSE”
   ethernetN.addressType = “static”
   ethernetN.address = “XX:XX:XX:XX:XX:XX″
   
   Where XX:XX:XX:XX:XX:XX is the new desired MAC address for the virtual machine.
   
   Note: For more information, see Editing files on an ESX host using vi or nano (1020302).
    
7. Register the virtual machine back to the inventory. For more information, see Registering or adding a virtual machine to the inventory (1006160).
8. Start the virtual machine.

Editing the .vmx file through the GUI

1. Shut down the virtual machine.
2. Right-click the virtual machine and click Remove from Inventory.
3. Download the .vmx configuration file for the virtual machine to your desktop using the Datastore Browser.
4. Open the .vmx configuration file with an plain text editor and add or change the following entries:
   
   ethernetN.checkMACAddress = “FALSE”
   ethernetN.addressType = “static”
   ethernetN.Address = “XX:XX:XX:XX:XX:XX″
   
   
   Where XX:XX:XX:XX:XX:XX is the new desired MAC address for the virtual machine.
    
5. Upload the new (modified) .vmx file back to the same location (datastore) using the Datastore Browser.
6. Copy the original .vmx file (using a name similar to vmname.vmx.old) for backup purposes.
7. Register the virtual machine back to the inventory. For more information, see Registering or adding a virtual machine to the inventory (1006160).
8. Start the virtual machine.