What are EUI-48 and EUI-64 addresses formed and used? Give me examples.

What are MA-L, MA-S and MA-M assignments?

I have read https://standards.ieee.org/develop/regauth/tut/eui48.pdf



And, understood nothing.

  • 1
    Do you have a specific question? It's hard to know where to begin without repeating the info you cited.
    – Ron Trunk
    Oct 21, 2015 at 17:38
  • 3
    EUI-48 is the link-layer address of ethernet devices (used almost nowhere else) EUI-64 is the link-layer address used pretty much everywhere else.
    – Ricky
    Oct 21, 2015 at 20:50

1 Answer 1


Historically, both EUI-48 and MAC-48 were concatenations of a 24-bit OUI (Organizationally Unique Identifier) assigned by the IEEE and a 24-bit extension identifier assigned by the organization with that OUI assignment (NIC). The subtle difference between EUI-48 and MAC-48 was not well understood; as a result, the term MAC-48 is now obsolete and the term EUI-48 is used for both (but the terms “MAC” and “MAC address” are still used).

In other words, EUI-48 and the MAC number of a device represent the same thing! Usually it is represented in 12 hex (e.g. 0023.a34e.abc9), equivalent to 48 bits or 6 bytes.

By implementing the EUI-64 (64-bit Extended Unique Identifier format), a host can automatically assign itself a unique 64-bit IPv6 interface identifier without the need for manual configuration or DHCP. So it's an IPv6 matter. Anyway, if you are interested about how it's calculated, it is applied to a MAC address like this:

The 48-bit MAC address is split in half, the hex group FFFE is inserted in the middle (after the 24th bit), and the seventh most-significant bit is inverted.


The MAC address    0021.86b5.6e10      (48 bit) becomes 
the EUI-64 address 0221.86ff.feb5.6e10 (64 bit)

MAC-Large, MAC-Small and MAC-Medium (abbreviated MA-L, MA-S and MA-M) have the all the same size. The names refer instead to number of bits within a MAC that remain governed by organization as opposed to the OUI bits governed by IEEE. If 24 bits of a MAC are governed by an organization/vendor/manufacturer, it is called a MAC-Large (this is a traditional scheme discussed so far). If 20 bits, it's MAC-Medium. If 12 bits, it's MAC-Small.

It addresses serious exhaustion problem of MAC addresses. Think how many devices are produced each day!

  • 2
    IPv6 SLAAC uses a modified EUI-64. There are LAN types which use EUI-64 as the layer-2 address, instead of EUI-48.
    – Ron Maupin
    May 31, 2016 at 22:43
  • 1
    I realize this is an old answer, but is there a source for the inverting of the 7th bit?Looking at the IEEE "Guidelines for Use of Extended Unique Identifier (EUI), Organizationally Unique Identifier (OUI), and Company ID (CID)" (tinyurl.com/y68bgdn8) Section "Mapping an EUI-48 to an EUI-64" (pg 15). There's no mention of the inversion, and I'm trying to determine if there are multiple mapping specs to follow.
    – rheone
    Nov 9, 2019 at 17:16
  • 3
    @RobertH.Engelhardt I was also curious about the bit inversion. Actually most tutorials and descriptions are wrong about it. The bit inversion is used to get the "Modified EUI-64" as described in RFC 4291 to acquire the interface identifier. Therefor the correct "EUI-64" value does not include the inversion. See also Understanding IPv6 EUI-64 Bit Address Feb 2, 2020 at 20:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy