What this tool does
Paste a MAC address — or just its first six hex digits — and this tool resolves the manufacturer of the network chipset behind it. Every Ethernet port, Wi-Fi radio, and Bluetooth interface ships with a 48-bit Media Access Control address burned in at the factory. The top 24 bits, called the OUI (Organizationally Unique Identifier), are leased from the IEEE to a specific company; the bottom 24 bits are that company's serial space. We match the OUI against the public IEEE registry and also decode the two flag bits hidden in the first octet, so you learn not just who made the interface but what kind of address you're looking at.
How the lookup works under the hood
First we normalise your input. Hardware vendors and operating systems print MAC addresses half a dozen ways — colon-separated, hyphen-separated, Cisco's dotted 3c5a.b400.0000 triplets, or bare hex. We strip the separators, validate that exactly twelve hexadecimal digits remain, and rebuild a single canonical form. From that we slice off the leading three octets as the OUI and look it up against a dataset derived from the IEEE's published assignments. We accept any of these and treat them identically: 3C:5A:B4:00:00:00, 3c-5a-b4-00-00-00, 3c5ab4.000000, or raw hex.
The IEEE actually issues blocks at three sizes. The classic MA-L grants a full 24-bit OUI (about 16.7 million addresses). The smaller MA-M and MA-S blocks carve the same prefix space more finely, which is why two devices can share the first few hex digits yet belong to different companies. Because of this, an OUI-only lookup is a strong hint rather than a guarantee for the very smallest allocations.
Reading the two flag bits
The least-significant two bits of the first octet carry meaning that trips up a lot of people:
- The U/L bit (locally administered). When set, the address was assigned by software, not by the factory — so there is deliberately no IEEE vendor behind it. This is the normal state for virtual-machine NICs, container interfaces, hand-assigned VLANs, and the randomised MACs that modern phones present to each new Wi-Fi network for privacy. If your lookup returns no vendor, check this bit first.
- The I/G bit (group / multicast). When set, the frame is destined for a group rather than a single interface.
ff:ff:ff:ff:ff:ffis the broadcast address; ranges like01:00:5e:…map IPv4 multicast and33:33:…map IPv6 multicast. These are not real device addresses, so vendor lookup on them is meaningless.
Common use cases and pitfalls
Network admins use OUI lookup to identify unknown devices on a switch port, audit a DHCP lease table, or spot rogue hardware. The biggest pitfall is treating a MAC as a stable identity: since iOS and Android now rotate randomised, locally-administered addresses by default, the “same” phone shows up under many MACs over time, and none of them resolve to Apple or Samsung. A second pitfall is reading too much into the vendor name — the OUI belongs to whoever made the silicon, which is often a chipset supplier rather than the brand on the box.
Frequently asked questions
Why does a MAC address resolve to no vendor?
Usually because the locally-administered bit is set, meaning the address was generated by software rather than registered with the IEEE — typical of randomised Wi-Fi clients, virtual machines, and hand-configured interfaces. A real registered OUI can also be too new or too niche to appear in the public dataset.
Can a MAC address identify a specific person or device?
No. The OUI only reveals the chipset manufacturer, not the model, owner, or location, and because phones rotate randomised MACs the same hardware presents many addresses over time. A MAC is not a reliable long-term identifier.
What is the difference between an OUI and a full MAC?
A MAC is 48 bits; the first 24 are the OUI assigned by the IEEE to a manufacturer, and the last 24 are chosen by that manufacturer to keep each interface unique. Vendor lookup only needs the OUI, so the first six hex digits suffice.
Data source
We forward your query to macvendors.com (free, no auth, with a roughly one-request-per-second rate limit). Their dataset tracks the public IEEE OUI registry. Responses are edge-cached for an hour.
JSON API
GET /api/mac/3C:5A:B4:00:00:00 returns the same payload plus the parsed-MAC flags. Example.
Related tools
Once you know what's on the wire, the DNS lookup and reverse DNS tool help map addresses to names, the what is my IP page shows how your own connection appears, and the IPv6 toolkit covers the address format that supersedes IPv4 on modern networks.