virtual mac adress range

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

src:http://serverfault.com/questions/40712/what-range-of-mac-addresses-can-i-safely-use-for-my-virtual-machines