MAC formatter and EUI-64 calculator

Colon (canonical EUI-48)

02:42:ac:11:00:02

Dash (Windows)

02-42-ac-11-00-02

Dot (Cisco)

0242.ac11.0002

Bare hex

0242ac110002

• reserved bitlocally-administered bit (U/L) is SET; the address was assigned locally, not by the vendor

Interface identifier (64 bits)

0042acfffe110002

fe80:: 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).