Modified EUI-64 Calculator
Construct and reverse a qualified hardware-derived interface identifier.
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About the Modified EUI-64 Calculator
Insert FF:FE into a 48-bit MAC and invert its U/L bit to create a modified EUI-64 interface identifier. Build the associated fe80:: link-local form and a supplied /64 prefix construction, or mechanically reverse a matching IPv6 identifier. A matching pattern does not prove the actual hardware address; modern privacy identifiers can use another mechanism.
How to use it
- Choose MAC conversion or reverse IPv6 conversion.
- Enter one complete MAC or an IPv6 address with the expected FF:FE pattern.
- Supply an IPv6 /64 prefix and review its normalized network.
- Unlock and copy or download the full identifier and assumptions.
Method and primary reference context
IPv6 addressing Appendix A, stateless autoconfiguration and stable-identifier recommendations.
Limitations
- Reverse conversion requires the inserted FF:FE pattern; the recovered value does not prove a device’s real MAC or vendor.
- SLAAC output combines a normalized /64 and an interface identifier. It does not test duplicate addresses, router advertisements, reachability or interface configuration.
- Stable privacy and temporary identifiers can differ from a hardware-derived EUI-64 identifier.
Privacy
On this device: nothing is sent
The supplied MAC, IPv6 address and prefix are processed on this device. Nothing is uploaded or stored.
Frequently asked questions
What do I get without a pass?
Without a pass, Modified EUI-64 Calculator shows useful labels with complete analysis figures and exports hidden. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
Which bit changes in the MAC?
The first byte is XORed with hexadecimal 02, toggling the universal/local bit. FF:FE is inserted between the original third and fourth bytes.
Why is a /64 required?
This construction uses 64 prefix bits and a 64-bit interface identifier. A different prefix length would not be the requested modified EUI-64 construction.
Does reverse conversion identify a device?
No. It reverses a matching bit pattern. Privacy identifiers and deliberately chosen addresses make hardware attribution unreliable.