The following terms are defined (either implicitly or explicitly) in IEEE Standard 802-2001 for use in referring to the various representations and formats of OUIs and the identifiers that may be created using them.
“The format of a MAC data frame in which the octets of any MAC addresses conveyed in the MAC user data field have the same bit ordering as in the Hexadecimal Representation.”[3] (See MAC data frame, MAC addresses) This appears from the context of the IEEE Standard 802-2001 to be another term for the 'Hexadecimal Representation' – i.e., “by interpreting the bits of the octet value as a binary numeral using the normal mathematical rules for digit significance.”[3] “The representation of a sequence of octet values in which the values of the individual octets are displayed in order from left to right, with each octet value represented as a two-digit hexadecimal numeral, and with the resulting pairs of hexadecimal digits separated by colons.
The order of the hexadecimal digits in each pair, and the mapping between the hexadecimal digits and the bits of the octet value, are derived by reversing the order of the bits in the octet value and interpreting the resulting bit sequence as a binary numeral using the normal mathematical rules for digit significance.”[3] The bit-reversed representation corresponds to the convention of transmitting the least-significant-bit of each byte first in serial data communications.
Example: An OUI consisting of the hexadecimal digits ACDE4816 would be represented as follows: The following figure shows the position of these bits in significance order: Notes: Ethernet users are used to seeing canonical form, such as in the output of the ifconfig command.
So for instance, an OUI whose canonical form is ACDE48 could be seen written as 357B12 if translation is done improperly or inconsistently.
Note: There were also IAB based CDI-40 sequences that were formed by combining the 36-bit IEEE assigned IAB base value with the 4-bit extension identifier assigned by the organization – e.g., if the IEEE assigned IAB base value is 0x0050C257A and the 4-bit extension identifier is 0xF, then the CDI-40 values generated by combining these two numbers are from 0x0050C257AF00 to 0x0050C257AFFF The IEEE now considers the label MAC-48 to be an obsolete term which was previously used to refer to a specific type of EUI-48 identifier used to address hardware interfaces (e.g., Network Interface Controllers and other network hardware) within existing IEEE 802 based networking applications and should not be used in the future.
Some of the storage systems in which an OUI based variant was used are Fibre Channel, and Serial Attached SCSI (SAS).
This addition requires either a shortened vendor-specific identifier field, or some OUI bits are assumed to be 0, such as when using EUI-64 Mapped format.
Unlike an OUI, which allows the assignee to assign values in various different number spaces (for example, EUI-48, EUI-64, and the various context-dependent identifier number spaces), the Individual Address Block could only be used to assign EUI-48 identifiers.
All other potential uses based on the OUI from which the IABs are allocated are reserved, and remain the property of the IEEE Registration Authority.