Organizationally unique identifier (OUI) refers to a 24-bit number assigned to a manufacturer or a vendor of a network device or station. They are globally unique identifiers assigned by the Institute of Electrical and Electronics Engineers (IEEE) Registration Authority.
OUI are typically used for uniquely identifying a particular device connected to the computer network through derived identifiers like the Medium Access Control (MAC) addresses. MAC addresses are of 6 octets ( 48-bits ). Among these, the first three octets of the addresses constitutes the OUI.
A 3-octet OUI is generally represented in hexadecimal notation separated by dashes (for example, 1F – 9E – A0) or by colons (for example, 1F : 9E : A0). However, there are other representations too.
The following figure depicts OUI in a MAC address −