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MAC formatter and EUI-64 calculator

Paste a MAC in any notation — get every other form, the multicast and locally-administered bits named, and the RFC 4291 EUI-64 with its fe80:: derivation.
accepts aa:bb:cc:dd:ee:ff · aa-bb-… · aabb.ccdd.eeff · bare hexConvertClearColon (canonical EUI-48)02:42:ac:11:00:02Dash (Windows)02-42-ac-11-00-02Dot (Cisco)0242.ac11.0002Bare hex0242ac110002

- reserved bitlocally-administered bit (U/L) is SET — the address was assigned locally, not by the vendor
Interface identifier (64 bits)0042acfffe110002fe80:: link-local (derived)fe80::42:acff:fe11:2

EUI-64 per RFC 4291 §2.5.1: the U/L bit is flipped, ff:fe is inserted between OUI and NIC halves. The fe80:: link-local row is the RFC 4291 derivation modern operating systems have largely replaced with random identifiers (RFC 8981) for privacy — shown because switches and older configs still derive it, not because your OS uses it.

- No OUI vendor lookup. The IEEE registry is a multi-megabyte dataset that changes weekly; a partial copy would guess, and a full copy is not worth your download. The first three octets are the OUI — look them up at the IEEE registry when you need the vendor.
- The U/L flip is part of the EUI-64 definition (the derived ID is locally-administered by construction); the tool shows both the input bits and the derived form.
- The fe80:: address is the standard derivation, shown for switches, static configs, and teaching — modern OSes randomize interface IDs by default (RFC 8981).
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48-bit BigInt math — every notation round-trips through the same value

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Canonical HTML: https://nutter.tools/network/mac-eui64
Markdown version: https://nutter.tools/network/mac-eui64/index.md
Plain-text version: https://nutter.tools/network/mac-eui64/index.txt
Agent index: https://nutter.tools/llms.txt