MAC Address Tools
Parse, classify and re-format a MAC / EUI-48 address.
Overview
The MAC address tools normalise, classify, and reformat a MAC / EUI-48 address. Paste any common form — colon-separated, dash-separated, Cisco dotted, or bare hex — and the tool returns every other format plus the universal/local bit, individual/group bit, and a vendor lookup for the leading OUI.
Network engineers reconciling addresses across vendor consoles, firmware developers parsing MAC strings, and anyone copying a MAC from a sticker into a DHCP reservation form benefits from a MAC address normaliser. Long-tail keywords covered: convert MAC address format online, validate MAC address syntax, and detect locally administered MAC.
How it works
A MAC address is 48 bits. The IEEE specifies several textual forms in IEEE 802 — aa:bb:cc:dd:ee:ff, aa-bb-cc-dd-ee-ff, aabb.ccdd.eeff (Cisco), and bare aabbccddeeff. All represent the same six octets. Two bits in the first octet have specific meaning: the low bit (I/G) is 1 for multicast / group addresses and 0 for unicast; the second-lowest bit (U/L) is 0 for a globally assigned address (real OUI) and 1 for a locally administered one.
EUI-64 extends MAC to 64 bits by inserting ff:fe between the OUI and the NIC-specific portion. IPv6 SLAAC historically derived an interface identifier from EUI-64, although modern stacks use randomised identifiers for privacy.
Examples
b8:27:eb:01:02:03→ unicast, globally administered, Raspberry Pi OUI.02:00:00:00:00:01→ unicast, locally administered (U/L bit set).01:00:5e:00:00:01→ multicast (I/G bit set), used by IPv4 multicast routing.ff:ff:ff:ff:ff:ff→ broadcast, special-case all-ones address.
FAQ
What is the canonical format?
There is no single standard. Linux and most network tools use lowercase colon-separated; Windows uses uppercase dash-separated; Cisco uses dotted quad. Use whichever your target system expects.
Is uppercase or lowercase preferred?
Hex is case-insensitive, so either parses. Lowercase is more common in current docs and configs.
Why is 01:00:5E:xx:xx:xx reserved?
That prefix is the multicast block reserved for mapping IPv4 multicast addresses onto Ethernet frames — the lower 23 bits of the IPv4 group address are copied into the lower 23 bits of the MAC.
Can two devices share a MAC?
Globally administered MACs are supposed to be unique. In practice, you sometimes see collisions on virtual NICs, cheap embedded gear, or after a hardware clone. Locally administered MACs are intentionally chosen by the operator.