Every NIC has a unique MAC address. but some of the Manufacturers provide configurable MAC Addresses.
To check the MAC address you have to go to the Command Prompt (Windows), then type ipconfig/all , in Linux you have to go to the terminal and type ifconfig
MAC is 6 bytes (48 bits) long.
First 3 bytes (24 bits) is OUI and is controlled by IEEE (http://www.ieee.org).
NIC manufacture buys OUI from IEEE.
Last 3 bytes (24 bits) is assigend by NIC maker.
NIC maker can be found by using OUI at IEEE website. (http://standards.ieee.org/regauth/oui/index.shtml)
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