MAC Formatter
Normalise separators and detect vendors
A MAC address identifies a network interface with 48 bits, usually written as six pairs of hex digits. The trouble is that no one agrees how to punctuate them: Linux and most standards use colons, Windows uses hyphens, Cisco uses three groups of four separated by dots, and plenty of systems store them bare with no separators at all.
The first three bytes are the Organisationally Unique Identifier, assigned by the IEEE to the manufacturer, which is why a MAC address often reveals who made the hardware. This tool normalises between the notations and reads the OUI prefix, which is what you need when comparing an address from a DHCP lease against one from a switch table.
How to use it
- Paste an address in any notationColons, hyphens, dots or nothing at all; upper or lower case. The separator is detected rather than required.
- Copy the format you needEvery notation is produced at once, so an address from a Windows adapter listing can go straight into a Linux config or a Cisco access list.
- Read the vendor prefixThe first three bytes identify the manufacturer, which is often enough to work out what an unknown device on a network actually is.
Frequently asked questions
Why do MAC addresses use different separators?
Convention rather than standard. IEEE documents use hyphens, Unix tooling settled on colons, and Cisco uses dotted quads of four hex digits. All describe the same 48 bits, so the differences matter only when something compares them as strings — which, unfortunately, plenty of software does.
What is an OUI?
The Organisationally Unique Identifier: the first 24 bits, assigned by the IEEE to a manufacturer. The remaining 24 bits are allocated by that manufacturer to individual interfaces. Because the registry is public, a prefix generally identifies who built the hardware.
Can a MAC address be changed?
Yes. Almost every operating system allows the address to be overridden in software, and this is routine rather than exotic — it is how virtual machines get addresses and how privacy features work. So a MAC address is an identifier, not proof of identity, and MAC-based access control is a weak control.
Why does my phone show a different MAC on every network?
MAC randomisation. iOS and Android now generate a distinct address per network by default, so that a device cannot be tracked across venues by its hardware address. It does mean MAC-based allow lists and DHCP reservations break unless the user disables randomisation for that network.
What do the special bits in the first byte mean?
The lowest bit of the first byte marks a multicast address when set, and unicast when clear. The next bit distinguishes a locally administered address from a globally unique one — a randomised or manually assigned address sets it, which is how you can tell at a glance that an address did not come from a manufacturer.