Home/Glossary/OUI (Organizationally Unique Identifier)

OUI (Organizationally Unique Identifier)

The first three bytes of a MAC address, assigned by IEEE to identify the manufacturer of a network device.

NetworkingAlso called: "mac vendor", "manufacturer id"

OUI helps identify device manufacturers from MAC addresses.

Structure

  • MAC address: 00:1A:2B:3C:4D:5E
  • OUI: 00:1A:2B (manufacturer)
  • Device-specific: 3C:4D:5E (unique to device)

Common OUIs

  • 00:50:56 - VMware
  • 08:00:27 - Oracle VirtualBox
  • 00:0C:29 - VMware
  • D8:9E:F3 - Apple
  • 00:15:5D - Microsoft Hyper-V

Use cases

  • Network inventory and asset management.
  • Identify unauthorized devices.
  • Troubleshoot network issues.
  • Detect virtual machines vs physical devices.
  • Security monitoring and analysis.

Lookup tools

  • IEEE OUI database (official).
  • MAC address vendor lookup websites.
  • Network scanning tools (nmap).

Privacy note

  • MAC addresses can track devices across networks.
  • Modern devices use MAC randomization.