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:
- What is the practical difference between MAC-48 and EUI-48 ?
- If EUI-48 is not "MAC Address", then how has it made MAC-48 obsolete ?
- 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?
Best Answer
There is no practical difference whatsoever.
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.
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
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.