What is the structure of a MAC address?

In universally administered addresses the first 24-bit, 28-bit or 36-bit identify the organization that issued the identifier.

MAC‌-64 examples:

• 00:09:8C:12:34:56:78:90, where 00:09:8C is MA-L block and 12:34:56:87:90 is interface controller specific
• CC:1B:E0:21:23:45:67:89, where CC:1B:E0:2 is MA-M block and 1:23:45:67:89 is interface controller specific
• 70:B3:D5:88:A1:23:45:67, where 70:B3:D5:88:A is MA-S block and 1:23:45:67 is interface controller specific