When you setup a network interface(s) for a Virtual Machine (VM) you must assign a MAC address to that interface. Much like an IP address, you must insure that the MAC address you assign does not conflict with any MAC address on your network. For a home network, it is simple enough to check the MAC address of each device, but in a larger environment with a large number of devices the task can be much more difficult. For either situation, there is an easy solution. A reserved range of MAC addresses exists, much like the reserved range of IP addresses for private use. It is technically referred to as a Locally Administered Address, or LAA. Where a MAC address is comprised of a 6 octet address (in hexadecimal form), the LAA range has the second LSB (Least Significant Bit) set to '1'. So valid ranges for LAA in hex form are:
x2-xx-xx-xx-xx-xx
x6-xx-xx-xx-xx-xx
xA-xx-xx-xx-xx-xx
xE-xx-xx-xx-xx-xx
You can assign your own value for 'x'. Of course, it must be in hexadecimal form, so valid values are 0-9, and A-F. Examples of valid LAAs are:
02-ab-cd-ef-12-34
d6-22-33-ff-ee-1a
etc... Something to think about: As you assign these address to your VMs, you want to be organized about your distribution model. For your home office, it is less relevant, as the number of MACs you will be assigning should be small. However, in a corporate office, you will need to interface with a large number of other users that may be attempting to do the same thing. Your IT department would be responsible for administering and assigning these addresses. I would assume you are probably a part of your IT department if you are reading this, so let me make a suggestion for a methodology to follow. I prefer to use an identifier of the individual, such as their phone extension, for part of the address, and then let them assign their own address for whatever VMs they create. For example, if John Doe is at extension 12345 (or his DID number ends in 12345) then I would assign him the MAC range of 22-01-23-45-xx-xx. He could decide his own designation for xx-xx. This would ensure that if conflicts arise, it will only be with his own system. On the server side, I prefer to identify the VM guest directly. I select one of the IP addresses that is assigned to the VM (assuming the IP address is static - for a server, it should be) and include that as part of the MAC address. For example, if my VM has an IP address of 10.123.234.222 it's MAC address would be aa-12-32-34-22-2x. X would then be assigned, one to each interface of the VM. As long as the VM did not have more than 16 NICs installed, it would be no problem. For the rare system with more than 16 NICs, I would change the first octet to 'ba', and follow the same approach for an additional 16 available addresses. To clarify, note that I selected a 'primary' NIC of the Virtual. It doesn't matter which one. For me, when installing a system for the first time, I usually only have one NIC that is installed in active to get the OS loaded and setup. I'll then add additional as needed. That is the NIC/MAC/IP combination that I refer to as my 'primary'. Of course, make sure you have all of this information centrally documented, just as you would for your static IP addresses.
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