EUI-48 to EUI-64 Conversion – Why Is EUI-48 to EUI-64 Conversion Deprecated Yet Used in IPv6?

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The IEEE Guidelines for Use of Extended Unique Identifier (EUI), Organizationally Unique Identifier (OUI), and Company ID (CID) [PDF] have a section titled, "Mapping an EUI-48 to an EUI-64". This section starts:

Mapping an EUI-48 to an EUI-64 is deprecated.

And yet, use of this algorithm for converting EUI-48 to EUI-64 in order to form "interface identifiers" seems to be codified in IPv6 standards (see appendix A).

The IEEE documentation states that the mapping algorithm is deprecated because,

Mapping an EUI-48 assigned with an MA-S/OUI-36 or MA-M assignment to an EUI-64 potentially creates a duplicate of an EUI-64 assigned with a different MA-S/OUI-36 or MA-M. The IEEE RA has taken appropriate actions to mitigate creation of duplicates based on this mapping but, to protect the integrity of EUI-64 identifiers, this mapping is deprecated.

  1. How is it possible that there could ever be a duplicate EUI-64 when using this algorithm, assuming all parties correctly and completely follow the IEEE standards?
  2. Why does IPv6 specify the use of this "deprecated" algorithm for converting EUI-48 to EUI-64? Or is use of this algorithm not technically, officially part of IPv6? (IMHO it is absolutely a de facto standard, in any case, but here I am asking about the de jure standard, so-to-speak.)

Best Answer

How is it possible that there could ever be a duplicate EUI-64 when using this algorithm, assuming all parties correctly and completely follow the IEEE standards?

There are 32,768 (including locally assigned 64-bit MAC, but excluding group MAC, addresses) that include a single 48-bit MAC address. That would limit the IEEE in building MAC addressing if it is allowed.

Why does IPv6 specify the use of this "deprecated" algorithm for converting EUI-48 to EUI-64?

You misunderstand one of the possible IPv6 ways of generating an IPv6 IID, which is using at 48-bit MAC address to generate a modified EUI-64 in the IPv6 address. It is not used as a layer-2 MAC address, but it could (is not mandated to) be used as the IID in a layer-3 IP address, and it is only one of many ways to try to generate a unique IID for a link. Do not confuse the network layers or which group controls the addressing for which protocols (IEEE for ethernet, et al that use MAC addressing, and the IETF that controls IP).

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