MAC Address Vendor Lookup (OUI)
Technical details
How the MAC Address Vendor Lookup Works
What the Tool Does
The MAC Address Vendor Lookup resolves the first 24 bits (OUI — Organisationally Unique Identifier) of a MAC address to the registered manufacturer by querying the IEEE Registration Authority's OUI database. It accepts MAC addresses in any common format (colon, dash, dot, no-separator) and returns the vendor name, registered address, and basic bit flags (locally-administered, multicast).
Common Developer Use Cases
Network engineers identify unknown devices on a LAN by reading the OUI from ARP or DHCP logs. Security analysts spot rogue or counterfeit hardware whose OUI doesn't match the claimed brand. IoT developers verify that newly-flashed firmware retained the correct MAC. Tooling that displays human-readable device labels (network maps, dashboards, packet captures) uses OUI lookup to enrich raw addresses.
Data Formats, Types, or Variants
Supported MAC formats: colon-separated (00:1A:2B:3C:4D:5E), dash-separated (00-1A-2B-3C-4D-5E), Cisco dot notation (001A.2B3C.4D5E), and unseparated hex (001A2B3C4D5E). The OUI is extracted as the first 6 hex characters. The bundled IEEE database (via the npm package oui-data, ~3.9MB) contains 39,000+ assignments and is loaded once when you open the tool — all subsequent queries are local.
Common Pitfalls and Edge Cases
Locally-administered MACs (the second-least-significant bit of the first octet is 1) are assigned by software, not by IEEE — they won't have a vendor match. Newer block sizes (MA-M, MA-S) use 28- or 36-bit prefixes; this tool only resolves classic 24-bit OUIs. Multicast addresses (least-significant bit of the first octet is 1) are flagged but lookups still attempt to find a vendor in the registered range.
When to Use This Tool vs Code
Use the browser tool for ad-hoc identification while staring at a packet capture or a network audit. In code, use the npm `oui` package server-side, Python's `manuf` or `netaddr.EUI.oui` modules, or the IEEE's downloadable CSV when you need bulk enrichment in a pipeline.