A complete guide to how the MAC Address Vendor Lookup identifies hardware manufacturers, and why importing the full IEEE registry requires a deliberate two-step process.
Launch the MAC Address Vendor Lookup →The MAC Address Vendor Lookup identifies which manufacturer produced a given network device based on its MAC (Media Access Control) address, by looking up the first six hexadecimal digits of the address, known as the OUI (Organizationally Unique Identifier), against a database of vendor assignments. The tool accepts MAC addresses in several common formats — colon-separated, dash-separated, dot-separated, or plain unformatted hex — and automatically normalizes whatever format you paste in.
It ships with a curated offline dataset of 144 common, publicly recognized vendor prefixes, which covers the overwhelming majority of everyday lookups without needing any additional setup. For more complete coverage, an optional "Load full registry" feature lets you import the official IEEE registry, containing more than 30,000 vendor assignments, through a deliberate two-step manual process explained in detail below.
Every network interface — the Wi-Fi or Ethernet hardware inside a computer, phone, printer, smart TV, or virtually any other network-connected device — has a MAC address: a 48-bit identifier, usually written as six pairs of hexadecimal digits, that's meant to be globally unique to that specific piece of hardware. Unlike an IP address, which can change depending on what network you connect to, a device's MAC address is typically burned into the hardware at the factory and stays constant.
The first half of a standard MAC address, the first three octets (six hex digits), is the OUI, and it identifies which organization registered that address block, almost always the manufacturer of the networking hardware itself. The IEEE Registration Authority (part of the Institute of Electrical and Electronics Engineers) is the official body responsible for assigning OUI blocks to companies, maintaining a public registry of exactly which organization owns which prefix. This tool's entire function is built on looking up a given OUI prefix against that registry (or a curated subset of it) to report back which organization it was assigned to.
The second half of the address, the remaining three octets, is assigned by the device manufacturer itself to make each individual device unique within their allocated OUI block, and carries no vendor information of its own — which is why vendor lookup tools only ever need to examine the first six hex digits.
The most natural-seeming way to implement a "load the full registry" feature would be for the page's JavaScript to directly fetch IEEE's published CSV file in the background and parse it automatically, the same way several other tools on this site fetch data from DNS resolvers or geolocation APIs. This was tried, confirmed not to work, and a different, deliberate approach was built instead.
The reason is the same CORS (Cross-Origin Resource Sharing) restriction explained in depth in the DNS Propagation Tool's documentation: a browser blocks JavaScript from reading the content of a cross-origin request unless the server being contacted explicitly sends an Access-Control-Allow-Origin header granting permission. IEEE's server, which was never designed with browser-based JavaScript consumption in mind, does not send that header, so any attempt to fetch() the registry file directly from this tool's own JavaScript gets silently blocked by the browser, even though the file itself is genuinely public and freely downloadable.
Rather than give up on the feature or attempt a fragile workaround, the tool uses a different, fully legitimate mechanism that CORS does not restrict: a real link that opens IEEE's official CSV in a new browser tab, triggering a completely normal, direct navigation to IEEE's server rather than a background script-driven request. Browser navigation (actually visiting a URL, as opposed to a script quietly fetching it behind the scenes) is not subject to CORS at all, since CORS exists specifically to govern what background scripts are allowed to read, not what pages a user is allowed to visit directly.
Because the direct-fetch approach was ruled out, importing the full registry requires two short, user-driven steps instead of one fully automated one. First, clicking "Open IEEE MA-L Registry CSV" opens IEEE's genuinely official CSV file in a new browser tab via a real navigation link, which the user then saves to their own computer using their browser's normal download or "Save As" functionality.
Second, the user selects that just-downloaded file using a standard file picker, and the tool reads its contents using the browser's built-in FileReader API, which lets JavaScript read a file's contents directly off the local disk once the user has explicitly chosen it through a file input element — a capability browsers do allow, since the user has to deliberately select the specific file themselves, which is a fundamentally different trust boundary than a script silently fetching data from a remote server in the background.
Once read locally, the CSV is parsed and merged into the tool's in-memory vendor database for the remainder of your browsing session, after which lookups against the full 30,000-plus entry registry work exactly like lookups against the smaller built-in dataset. IEEE also separately publishes two smaller supplementary registries (MA-M and MA-S) covering additional, newer, or smaller block vendor assignments, and the tool supports selecting multiple files at once in the file picker step if you want to import all three registries together.
Given that the full registry import process exists, it's worth explaining why the tool doesn't just ship with the complete 30,000-plus entry registry baked in from the start. The curated 144-entry dataset focuses specifically on the vendors most commonly encountered in everyday device identification — major computer, networking equipment, phone, and consumer electronics manufacturers — which covers the overwhelming majority of real-world lookups without requiring any additional setup at all.
This keeps the tool's initial page weight small and the default experience instant, while the full-registry import remains available as an optional, deliberate step for the smaller set of situations where someone genuinely needs comprehensive coverage, such as identifying an unusual or less common device, or doing systematic network inventory work covering a wide variety of hardware vendors.
00:1A:2B:3C:4D:5E, 00-1A-2B-3C-4D-5E, or 001A2B3C4D5E.Looking up 3C:5A:B4:12:34:56 would extract the OUI 3C:5A:B4 and check it against the loaded vendor dataset, reporting back the specific manufacturer that IEEE assigned that prefix to, if it exists in whichever dataset (curated or full registry) is currently loaded.
All MAC address lookups happen entirely on your device, whether using the built-in curated dataset or an imported full registry file. The file-import process reads a file you've explicitly downloaded and selected yourself using your browser's local FileReader API, and that file's contents never leave your device or get uploaded anywhere.
No MAC address you look up, and no vendor registry file you import, is ever transmitted to, logged by, or stored on any NexTechTools server.
IEEE's server does not grant the CORS permission required for a background script to fetch its data directly, which is a restriction on IEEE's server configuration, not something this tool's code can work around. The two-step download-then-select process uses a real browser navigation and a user-selected local file instead, both of which are mechanisms CORS does not restrict.
Yes — it's a genuinely official, publicly published CSV file directly from IEEE's own registration authority website, the same organization that assigns these vendor codes in the first place.
Yes, in principle. Most operating systems allow a device's reported MAC address to be manually overridden (a practice sometimes called MAC spoofing), which would cause this tool to correctly report whatever vendor was assigned to the spoofed prefix, not the device's actual original manufacturer. For the vast majority of everyday, non-adversarial situations, though, devices report their genuine factory-assigned MAC address.
MAC addresses include a bit indicating whether they were assigned by the manufacturer under an IEEE-registered OUI (universally administered) or manually set by software or a system administrator (locally administered), which is useful context when a lookup against a vendor database doesn't return a match, since locally administered addresses are not tied to any registered vendor prefix at all.