IPv6 uses a 64-bit Modified Extended Unique Identifier (Modified EUI-64) in the lower half of some IPv6 addresses. A Modified EUI-64 is an EUI-64 with the U/L bit inverted. There are other identifiers that may be formed using the OUI but those listed above are the most commonly used. Mapping an EUI-48 to an EUI-64 is deprecated. The mapping is described here for historical reasons. Other identifiers, such as MAC-48 and EUI-48 values, can be contained within a larger identifier or 'container', such as EUI-64, by creating the larger identifier through a process of combining the smaller identifier with specified values placed in specified bit-positions within the larger identifier – this process is known as 'encapsulation' and is provided for the purpose of easing the transition from MAC-48 and EUI-48 to EUI-64 and to provide a mechanism for the conversion of MAC-48 and EUI-48 identifiers to EUI-64 in such a way that duplicate or conflicting values are avoided. Encapsulation of MAC-48 within EUI-64 Example:  Assuming that an organization has registered the OUI of AC-DE-48 and that the organization has created the MAC-48 value of AC-DE-48-23-45-67 by concatenating the extension identifier 23-45-67, this MAC-48 identifier has the following binary transmission order: The same MAC-48 identifier after encapsulation within an EUI-64 has the following transmission order: The same MAC-48 identifier after encapsulation within an EUI-64 has the following significance order: Encapsulation of EUI-48 within EUI-64 example:  Assuming that an organization has registered the OUI of AC-DE-48 and that the organization has created the EUI-48 value of AC-DE-48-23-45-67 by concatenating the extension identifier 23-45-67, this EUI-48 identifier has the following format in significance order: The same EUI-48 identifier after encapsulation within an EUI-64 has the following format in significance order: Encapsulation of MAC-48 or EUI-48 within modified EUI-64 example:  In the encapsulation within a Modified EUI-64 a MAC-48 is treated as an EUI-48 and the U/L bit is inverted. Assuming that an organization has registered the OUI of AC-DE-48 and that the organization has created the MAC-48 or EUI-48 value of AC-DE-48-23-45-67 by concatenating the extension identifier 23-45-67, this MAC-48 or EUI-48 identifier has the following format in significance order: The same MAC-48 or EUI-48 identifier after encapsulation within a Modified EUI-64 has the following format in significance order:  Network Address Authority (NAA) Name_Identifier formats define the first nibble (4 bits) to define the format of the identifier:  This encapsulation is used in Fibre Channel and SAS, and is also supported in iSCSI in RFC 3980.