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organization unique identifier (OUI)

The Organization Unique Identifier (OUI) is part of the MAC address. It is a three octet long data field allocated by IEEE for manufacturer identification.

The 24 bits of the OUI code are the first three octets of the MAC address, which are reserved for manufacturer identification. Each manufacturer has its own OUI codes by which it can be identified. In this address range, each manufacturer can use the following 24 bits for individual identification of the network card.

Structure of MAC addresses

Structure of MAC addresses

Depending on the application, the OUI data field can also be followed by a 12-bit Individual Address Block (IAB) or the two-octet PID data field for the Protocol Identifier (PID).

In order to guarantee unique address assignment worldwide, IEEE has extended the address range for MAC addresses from 48 bits to 64 bits with the Extended Unique Identifier (EUI). The corresponding format is called EUI-64.

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Englisch: organization unique identifier - OUI
Updated at: 27.05.2011
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