A 24-bit number that uniquely identifies a vendor or organization is called?

• A. Organizationally Unique Identifier
• B. User ID
• C. Network ID
• D. Vendor Prefix

Answer: (A)

Organizationally Unique Identifier is the 24-bit field used in MAC addresses that uniquely identifies a vendor or organization. Assigned by IEEE to each registered company, the OUI forms the first portion of a 48-bit MAC address, with the remaining bits allocated by the vendor to identify a specific device. This setup lets every network interface have a globally unique hardware address tied to its manufacturer. The other options describe different concepts (a User ID for people, a Network ID for IP-related addressing, or a term like Vendor Prefix that isn’t the formal IEEE name), so they don’t fit the specified role of identifying the vendor in hardware addressing.