Do you really think that there could be a duplicate MAC address if you use "macchanger" an your Linux machine? There are 2⁴⁸ possible 48 bit numbers and there is a limited number of those as MAC addresses, but it still is in the trillions, and the MAC addresses would be only scoped locally.

I have thought about this before, and the industry has been wondering about running out of addresses. Hence, MAC48 is now obsolete and we are now moving towards EUI-64. However, as I studied for Network+ it was interesting to see what exactly would happen if you were to have a duplicate. Actually, the local switch would get confused and flap back and forth between the ports that store the addresses. The only way to figure that out is to get on the Switch itself and see the error message. You would not be able to tell from anything on your PC, whether it be Unix based or Windows based. The Internet just would not work.

Therefore, this is maybe some reason why IT always tells us to restart our computers when we have issues.