An Organizationally Unique Identifier (OUI) is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers, Incorporated (IEEE) Registration Authority. This identifier uniquely identifies a vendor, manufacturer, or other organization (referred to by the IEEE as the “assignee”) globally or worldwide and effectively reserves a block of each possible type of derivative identifier (such as MAC addresses, group addresses, Subnetwork Access Protocol protocol identifiers, etc.) for the exclusive use of the assignee. The OUI is subsequently used by the assignee to create particular instances of these identifiers for various purposes, such as the identification of a particular piece of equipment (e.g., a network interface controller (NIC)) or the identification of a network protocol, and for use in various computer hardware products, including MAC addresses for Ethernet and other NICs (network interface cards), World Wide Names for Fibre Channel host bus adapters, and other Fibre Channel and Serial Attached SCSI devices.
In MAC addresses, the OUI is combined with a 24-bit number (assigned by the owner or 'assignee' of the OUI) to form the address. The first three octets of the address are the OUI.
Read more about Organizationally Unique Identifier: Representational and Formatting Conventions / Standards (IEEE 802-2001), Format, Encapsulating, Individual Address Block, Compare To
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