EUI48 vs EUI64

refer to answer here:

https://networkengineering.stackexchange.com/questions/23566/what-are-eui-48-and-eui-64

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 bit is inverted.

Example:

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