EUI-64 Calculator
Convert a 48-bit MAC address into its modified EUI-64 interface identifier and the resulting IPv6 address.
Inputs
EUI-64 Interface ID
021a:2bff:fe3c:4d5e
Resulting IPv6 Address
2001:db8:acad:1:21a:2bff:fe3c:4d5e
Universal/Local Bit Flipped To
1 (universal)
Vendor OUI
00:1a:2b
Step by step
Values used
MAC address = 00:1a:2b:3c:4d:5e; Network prefix (first four groups) = 2001:db8:acad:1
EUI-64
ff:fe is inserted between the OUI and the device identifier, and bit 7 of the first octet (the universal/local bit) is inverted.
EUI-64 Interface ID
= 021a:2bff:fe3c:4d5e
Resulting IPv6 Address
= 2001:db8:acad:1:21a:2bff:fe3c:4d5e
Universal/Local Bit Flipped To
= 1 (universal)
Vendor OUI
= 00:1a:2b
How it works
Modified EUI-64 splits the MAC in half, inserts ff:fe in the middle and flips the universal/local bit so that a globally unique MAC produces an identifier marked as universally administered. This is the identifier SLAAC generates by default, so being able to derive it by hand is how you predict an address before a host boots and how you recognise one in a log.
Formula
EUI-64
ff:fe is inserted between the OUI and the device identifier, and bit 7 of the first octet (the universal/local bit) is inverted.
- OUI
- First 24 bits of the MAC, identifying the vendor
- ff:fe
- Fixed padding that stretches 48 bits to 64
Frequently Asked Questions
How is EUI-64 calculated?
ff:fe is inserted between the OUI and the device identifier, and bit 7 of the first octet (the universal/local bit) is inverted. Modified EUI-64 splits the MAC in half, inserts ff:fe in the middle and flips the universal/local bit so that a globally unique MAC produces an identifier marked as universally administered.
Why does EUI-64 matter?
This is the identifier SLAAC generates by default, so being able to derive it by hand is how you predict an address before a host boots and how you recognise one in a log.
What values do I need to enter?
This calculator takes 2 inputs: MAC address, Network prefix (first four groups). The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.