Aaron Graves, PhDude (Replica)

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eui 64 calculator

Posted on February 16, 2026 by Admin

EUI-64 MAC to IPv6 Interface ID Calculator

Convert a 48-bit MAC address into a modified EUI-64 identifier. Optionally provide an IPv6 /64 prefix to generate a complete SLAAC-style IPv6 address.

This tool uses the modified EUI-64 process: insert ff:fe in the middle and flip the U/L bit of the first octet.

What Is EUI-64?

EUI-64 is a method for creating a 64-bit interface identifier, usually from a 48-bit MAC address. In IPv6, this identifier can be combined with a 64-bit network prefix to form a full 128-bit address. Historically, this was common with Stateless Address Autoconfiguration (SLAAC).

When engineers mention “modified EUI-64,” they specifically mean the process used for IPv6 interface IDs. It is “modified” because one bit in the first byte is inverted to indicate universal/local scope.

How the EUI-64 Conversion Works

1) Normalize the MAC address

The calculator accepts formats like:

  • 00:1C:42:2E:60:4A
  • 00-1C-42-2E-60-4A
  • 001c.422e.604a

They all represent the same 48-bit value.

2) Flip the U/L bit in the first octet

The first byte is XORed with 0x02. If the original first byte is 00, it becomes 02. This is a key EUI-64 rule used for IPv6 interface construction.

3) Insert FF:FE in the middle

Take the first three MAC bytes, then add FF:FE, then append the final three MAC bytes.

MAC:      00:1C:42:2E:60:4A
Flip bit: 02:1C:42:2E:60:4A
EUI-64:   02:1C:42:FF:FE:2E:60:4A

4) Build the interface ID (and optional full IPv6)

The 8 bytes are grouped as four IPv6 hextets:

021c:42ff:fe2e:604a

If you also provide a prefix such as 2001:db8:abcd:12::/64, the resulting full IPv6 address is:

2001:db8:abcd:12:21c:42ff:fe2e:604a (compressed notation may vary)

Why This Still Matters

  • IPv6 troubleshooting: Quickly verify whether an interface ID was derived from a MAC.
  • Network labs and training: Helpful for CCNA/CCNP-level IPv6 practice.
  • Embedded/IoT systems: Some environments still derive IPv6 identifiers from hardware addresses.
  • Forensics and operations: Recognize and validate addressing patterns in packet captures and logs.

Security and Privacy Note

Using MAC-derived interface IDs can expose hardware identity patterns. Modern systems often prefer privacy extensions (temporary/randomized IPv6 addresses) to reduce tracking risk. So while EUI-64 is still important for understanding and diagnostics, many production endpoints avoid using it as their primary public identifier.

Common Input Mistakes

  • Entering a MAC with fewer or more than 12 hex characters.
  • Using invalid hex symbols (only 0-9 and a-f are allowed).
  • Providing a prefix that is not /64 for SLAAC-style composition.
  • Supplying malformed IPv6 strings with multiple :: compressions.

Quick FAQ

Is this the same as plain EUI-64 from IEEE?

For IPv6 addressing, people usually mean the modified process (U/L bit flip + FF:FE insertion). That is what this calculator performs.

Can I use this for link-local addresses?

Yes. The tool also shows a derived fe80::/64 link-local style address built from the calculated interface ID.

Do all devices still use EUI-64 for global IPv6 addresses?

No. Many modern OSes use privacy addresses or stable-but-randomized identifiers instead of direct MAC-derived IDs.

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