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As mentioned at Wikipedia,

The distinction between EUI-48 and MAC-48 identifiers is purely nominal: MAC-48 is used for network hardware; EUI-48 is used to identify other devices and software. (Thus, by definition, an EUI-48 is not in fact a "MAC address", although it is syntactically indistinguishable from one and assigned from the same numbering space.)

The IEEE now considers the label MAC-48 to be an obsolete term, previously used to refer to a specific type of EUI-48 identifier used to address hardware interfaces within existing 802-based networking applications, and thus not to be used in the future. Instead, the proprietary term EUI-48 should be used for this purpose.

In addition, the EUI-64 numbering system encompasses both MAC-48 and EUI-48 identifiers by a simple translation mechanism. To convert a MAC-48 into an EUI-64, copy the OUI, append the two octets FF-FF and then copy the organization-specified extension identifier. To convert an EUI-48 into an EUI-64, the same process is used, but the sequence inserted is FF-FE. In both cases, the process can be trivially reversed when necessary. Organizations issuing EUI-64s are cautioned against issuing identifiers that could be confused with these forms. The IEEE has a target lifetime of 100 years for applications using MAC-48 space, but encourages adoption of EUI-64s instead.

IPv6 — one of the most prominent standards that uses a Modified EUI-64 — treats MAC-48 as EUI-48 instead (as it is chosen from the same address pool) and toggles the U/L bit (as this makes it easier to type locally assigned IPv6 addresses based on the Modified EUI-64). This results in extending MAC addresses (such as IEEE 802 MAC address) to Modified EUI-64 using only FF-FE (and never FF-FF) and with the U/L bit inverted.

Based on this, I have following questions:

  1. What is the practical difference between MAC-48 and EUI-48 ?
  2. If EUI-48 is not "MAC Address", then how has it made MAC-48 obsolete ?
  3. If MAC-48 is burned-in-address and is stored in ROM of NIC, then, does that mean, when we change MAC address with software, it is EUI-48 that is being changed?
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Dec 25 '18 at 8:32
  • @RonMaupin Thanks for reminding, have accepted.. – GypsyCosmonaut Dec 25 '18 at 8:54
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1.What is the practical difference between MAC-48 and EUI-48 ?

2.If EUI-48 is not "MAC Address", then how has it made MAC-48 obsolete ?

3.If MAC-48 is burned-in-address and is stored in ROM of NIC, then, does that mean, when we change MAC address with software, it is EUI-48 that is being changed?

  1. There is no practical difference whatsoever.

  2. It is just that IEEE no longer calls them by the old name (MAC-48), it now calls them by the new name (EUI-48). The reason for this is that they are now used for more things than just media access addressing.

  3. In the up-to-date terminology, we'd say that the device has a burned-in EUI-48 which you have changed in software. The point of the change is that the device doesn't need to be a network card doing media access, and we'd like terminology which doesn't presume it is.

Other than interface cards, what are EUIs used for? IEEE says

The 48-bit Extended Unique Identifier (EUI-48) [...] are globally unique identifiers used for identification of objects. Objects may be a hardware device (e.g., a network interface), a function (e.g., to identify a clock function) and similar applications. [...] most commonly used for IEEE 802 universally unique MAC addresses.

In essence the IEEE is just being a source for unique numbers. Mostly people use them for MAC addresses, but you could use them for serial numbers of cars, or museum object IDs.

For analogy, in internet addressing, we no longer speak of "subnet mask", we say "netmask" because everything is now CIDR. We no longer speak of "Class B", we say "/16". On the equipment, there's still 255.255.0.0 somewhere, but we think of it very slightly differently.

  • Replying to your 2nd point.. "The reason for this is that they are now used for more things than just media access addressing". What else does EUI-48 bring that MAC-48 could not offer. This is what I want to understand. The difference. – GypsyCosmonaut May 22 '18 at 15:35
  • There is no fundamental difference. "MAC" is a term tied to ethernet. EUI is not pinned to anything. ('tho EUI-64 would be preferred. Ethernet will always require a 48bit address.) – Ricky Beam May 22 '18 at 18:17
  • The difference is that if it's not a network interface it doesn't have a MAC address. I edited the answer with IEEE statement about clock functions; and suggestion of cars and museum object ids. – jonathanjo May 22 '18 at 21:02

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