Computer Support - Understanding Ethernet Addresses
Every Ethernet interface has a unique hardware address, which is commonly know as its physical address or Media Access Control (MAC) address. This address is expressed as 12 hexadecimal digits. Because each hexadecimal digit is four bits long, the complete MAC address is 48 bits long. The leftmost six digits specify the interface's original equipment manufacturer (OEM) and the rightmost six digits specify a unique number that distinguishes this interface from all others in the same OEM group. Sometimes you'll see the address written unhyphenated (0020AFF9AC65), sometimes you'll see it with a hyphen separating the OEM from the serial number (0020AF-F9AC65), and sometimes you'll see a hyphen separating each byte (00-2--AF-F(-AC-65).