EUI-64 Calculator
Convert a 48-bit MAC address to a modified EUI-64 interface identifier and build the IPv6 link-local address.
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Turn a MAC address into a modified EUI-64 interface identifier and IPv6 link-local address.
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Generate a modified EUI-64 interface ID
Modified EUI-64 is the standard method for deriving a 64-bit IPv6 interface identifier from a 48-bit MAC address. The process inserts the hexadecimal value FFFE between the first three and last three bytes of the MAC, and flips the seventh bit of the first byte, known as the universal or local bit. This calculator performs both steps and shows the resulting interface identifier, as well as the full IPv6 link-local address formed by prepending the fe80 prefix.
For example the MAC 00:1A:2B:3C:4D:5E becomes the interface identifier 021a:2bff:fe3c:4d5e, where the first byte changes from 00 to 02 because of the flipped bit.
Why EUI-64 is used
IPv6 stateless address autoconfiguration historically used EUI-64 to let a device build its own address from its hardware MAC without a DHCP server. Understanding the transformation is important for network engineers reading IPv6 addresses, troubleshooting autoconfiguration, and studying for certifications, where the bit-flip and FFFE insertion are frequently tested.
Modern systems often use randomised privacy addresses instead of EUI-64 to avoid exposing the hardware MAC, but EUI-64 remains part of the standard and is still seen on many networks. All calculation happens locally in your browser.
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Frequently Asked Questions
What is modified EUI-64?
It is the method of building a 64-bit IPv6 interface identifier from a 48-bit MAC by inserting FFFE in the middle and flipping the universal or local bit.
Why is the seventh bit flipped?
Flipping the universal or local bit of the first byte inverts its meaning so that a globally unique MAC produces a conventionally formatted interface identifier.
What is the link-local address?
It is the IPv6 address in the fe80::/10 range that every interface forms for communication on its local link, here built from the EUI-64 identifier.
Do modern devices still use EUI-64?
Many now use randomised privacy addresses to hide the hardware MAC, but EUI-64 is still part of the IPv6 standard and appears on numerous networks.
Does it work with a Cisco dotted MAC?
Yes. The tool strips any separators, so colon, hyphen, dotted and bare MAC formats all work as input.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Enter a MAC address to generate its EUI-64 interface ID and link-local address.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
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NetworkCheck which common ports respond on a host and understand what each exposed service means. Scan only systems you are authorised to test.
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NetworkAnalyze DNS records (TXT, SPF) for security gaps.
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NetworkCheck client-server compatibility for TLS versions.