Ubuntu – wlan and macchanger

After determining that we could use the computer's original MAC address to spoof itself, and that changing just one character could break it, a Google search for "valid MAC address" turned up a wealth of information.

There are actually 4 sets of Locally Administered Address Ranges that can be used on your network without fear of conflict, assuming no one else has assigned these on your network:

x2-xx-xx-xx-xx-xx
x6-xx-xx-xx-xx-xx
xA-xx-xx-xx-xx-xx
xE-xx-xx-xx-xx-xx

Replacing x with any hex value.

Useful translation of the wikipedia version: "Universally administered and locally administered addresses are distinguished by setting the second least significant bit of the most significant byte of the address. If the bit is 0, the address is universally administered. If it is 1, the address is locally administered. In the example address 02-00-00-00-00-01 the most significant byte is 02h. The binary is 00000010 and the second least significant bit is 1. Therefore, it is a locally administered address.[3] The bit is 0 in all OUIs." – Adam Brand

In universally administered MAC addresses, the three most significant bytes are preassigned to specific companies/vendors.

A MAC address validator can be found at http://sqa.fyicenter.com/Online_Test_Tools/MAC_Address_Format_Validator.php.