How to enable duplicate MAC addresses on Virtual Server 2005R2

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Just wanted to pass this one a long, is embarrassingly enough I actually learned about this on one of our public newsgroups.  By default Virtual Server 2005R2 will detect if you have virtual machines on the same box configured with duplicate MAC addresses and stop you from starting them up at the same time.  Now for 90% of cases this is the correct thing to do.  However, if you really, really, really know what you are doing and need to boot virtual machines with the same MAC address you can do the following:

  1. Stop the Virtual Server service (either use the services management console or run "net stop "virtual server"". 

  2. Use notepad to open "C:Documents and SettingsAll UsersApplication DataMicrosoftVirtual Serveroptions.xml" (where C: is one of your system drive is). 

  3. Locate the <virtual_network> </virtual_network> section and add:

    <duplicate_mac>
       <isAllowed type="boolean">true</isAllowed>
    </duplicate_mac>

  4. When you are done save the file and restart the Virtual Server service. 

You can now start virtual machines with duplicate MAC addresses, but once again please be careful when doing this.

Cheers,
Ben