Enter the first 6 nibbles of the MAC address into the IEEE public registry of OUI or company_ids.
http://standards.ieee.org/regauth/oui/index.shtml
The cases where this wont work:
* If its a locally administered address, as evidenced by the 41st bit of the 48 bit MAC
* Its not spoofed and set to something else on the card
* is some reserved number such as 01:00:5e, which is meant for multicast addressing
All in all an interesting exercise...
