How are MAC address prefixes assigned?
So that no address is ever handed out twice, a single organisation distributes prefixes: the IEEE. Each vendor buys a block, then numbers its own devices inside that block.
One registry, kept by the IEEE
The IEEE Registration Authority assigns organisation identifiers, historically called OUIs (Organizationally Unique Identifiers). A vendor files a request, pays a registration fee, and receives a prefix reserved for it permanently.
These assignments are public: the oui.txt file published by the IEEE lists every prefix with the name and postal address declared by the organisation. MAClens uses that official source directly, with no third-party service in between.
Three block sizes: MA-L, MA-M, MA-S
Not every vendor needs the same volume of addresses, so the IEEE offers three sizes:
- MA-L (large) — the first 24 bits are fixed, which is the three-byte prefix everyone calls an “OUI”. That leaves roughly 16.7 million addresses to the vendor. This is the classic block, and the only one directly readable in an address.
- MA-M (medium) — 28 fixed bits, about one million addresses. Several organisations then share the same three-byte prefix.
- MA-S (small) — 36 fixed bits, leaving 16,777,216 / 4,096, that is 4,096 addresses. Suited to small manufacturers and limited product runs.
Practical consequence: a three-byte prefix is not always enough to point at one single company. For an MA-M or MA-S block, the main registry often shows the name of an intermediary or a management entity rather than the brand printed on the device.
From prefix to device
Once the block is granted, the vendor alone is responsible for the remaining bits. They are usually assigned sequentially per production site, which is why devices from the same batch carry very similar addresses.
One manufacturer often owns dozens of prefixes, collected over the years through acquisitions and product lines. Conversely, a Wi-Fi chip bought from a supplier may carry that supplier’s prefix rather than the brand of the finished device.
Why the name found does not always match the brand
Several reasons explain a surprising result:
- the prefix belongs to the component maker, not to the brand of the device;
- the company was acquired or renamed without updating the registry;
- the address was changed, randomised, or created by virtualisation software;
- the address falls in a range reserved by the standards, described on the special addresses page.
When no prefix matches, the most common explanation is simply that the address was never assigned by the IEEE. Test an address to see what the official registry says.