In the MAC address 00:90:69:9f:ea:46, what represents the Organizationally Unique Identifier (OUI)?

69:9f:ea:46 represents the last four octets, which is the vendor-assigned extension, not the OUI.

00:90:69:9f represents the first four octets, which includes part of the device identifier, not solely the OUI.

9f:ea:46 represents the last three octets, which is the vendor-assigned extension, not the OUI.

The Organizationally Unique Identifier (OUI) is the first 24 bits (the first three octets) of a MAC address, which uniquely identifies the manufacturer or vendor of the network interface. In the given MAC address 00:90:69:9f:ea:46, '00:90:69' constitutes the OUI.