Introduction
Every network interface has a 48-bit MAC address burned into its hardware. The first 24 bits (the OUI, or Organizationally Unique Identifier) identify the manufacturer. This tool looks up the OUI against a built-in database of common vendors, decodes the U/L and I/G bits from the first byte, and generates random MAC addresses for testing. Paste any MAC address in colon, hyphen, or dot notation and the vendor appears instantly. No data leaves your browser.
What this tool does
- Look up the OUI (first 3 bytes) of any MAC address against a curated database of common vendors including Intel, Apple, Cisco, Dell, HP, VMware, Samsung, Google, and Microsoft
- Accept MAC addresses in any common format: colon-separated (`00:1A:2B:3C:4D:5E`), hyphen-separated (`00-1A-2B-3C-4D-5E`), dot-separated (`001A.2B3C.4D5E`), or raw hex (`001A2B3C4D5E`)
- Decode the first byte to show the I/G bit (bit 0: unicast vs multicast) and U/L bit (bit 1: universally administered vs locally administered)
- Display the first byte in binary so you can see exactly which bits are set
- Generate random MAC addresses with an optional real vendor OUI prefix, or with the locally administered bit set for testing purposes
- Run entirely client-side with a built-in OUI database, requiring no network access
How this tool works
The tool strips all non-hexadecimal characters from the input and uppercases the result. It requires exactly 12 hex characters (6 bytes). The first 6 characters form the OUI, which is looked up in a curated dictionary mapping OUI prefixes to vendor names. If the OUI is not in the database, the tool reports 'Unknown vendor'.
The first byte is parsed as an integer and converted to an 8-bit binary string. Bit 0 (the least significant bit) is the I/G (Individual/Group) flag: 0 means unicast, 1 means multicast. Bit 1 is the U/L (Universal/Local) flag: 0 means the address is universally administered (assigned by the IEEE), 1 means it is locally administered (assigned by the organization, not the IEEE).
The random MAC generator has two modes. With 'Use a real vendor OUI prefix' enabled, it picks a random OUI from a list of common vendors and appends 3 random bytes. Without it, the generator sets the U/L bit (bit 1 = 1) and clears the I/G bit (bit 0 = 0) to produce a locally administered unicast address, which is safe for testing and will not collide with any real device.
How MAC addresses work (IEEE Std 802-2014)
MAC addresses are 48-bit identifiers defined in IEEE Std 802-2014, which specifies the assignment and structure of MAC addresses for IEEE 802 networks. The first 24 bits are the OUI (Organizationally Unique Identifier), assigned by the IEEE Registration Authority. The remaining 24 bits are the NIC-specific portion, assigned by the manufacturer.
The IEEE maintains a public OUI registry that maps each assigned OUI to its organization. The registry is updated monthly. This tool includes a curated subset of the most common vendor OUIs. For a complete lookup, you can download the full registry from the IEEE website.
The first byte of a MAC address carries two flag bits. Bit 0 (LSB) is the I/G bit: when set, the address is a multicast destination. For example, `01:00:5E:xx:xx:xx` is the multicast range for IPv4 (RFC 1112). Bit 1 is the U/L bit: when set, the address is locally administered rather than globally unique. Virtual machines and containers often use locally administered addresses (e.g. VMware's `00:50:56` range, or Docker's `02:42:xx:xx:xx:xx` with the U/L bit set).
For generating unique identifiers in other contexts, see the UUID Generator, Snowflake ID Generator, and NanoID Generator.
How to use this tool
- Paste a MAC address in any format (colons, hyphens, dots, or raw hex). The tool strips separators automatically
- The output shows the normalized colon-separated format, the OUI (first 6 hex chars), and the vendor name
- Check the Type field to see whether the address is Universally Administered (UAA) or Locally Administered (LAA)
- Check the Transmission field to see whether the address is unicast or multicast
- The first byte is shown in binary with the I/G and U/L bits labeled
- To generate a random MAC for testing, use the MAC Randomizer. Enable 'Use a real vendor OUI prefix' for realistic addresses, or leave it off for locally administered test addresses
Real-world examples
Identifying a device on your network
You see an unknown device at `00:1A:11:3F:2C:8A` in your router's DHCP table. Paste it into the tool. The OUI `001A11` maps to Apple, Inc. The address is universally administered (U/L bit = 0) and unicast (I/G bit = 0), confirming it is a real Apple device with a factory-assigned MAC.
Detecting a virtual machine
A device at `00:0C:29:4D:1E:7B` appears in your network scan. The OUI `000C29` maps to VMware, Inc. This tells you the device is a virtual machine running on a VMware host, not a physical machine. The U/L bit is 0 because VMware has its own IEEE-assigned OUI range.
Generating a test MAC for a container
Leave 'Use a real vendor OUI prefix' unchecked and click Generate random MAC. The tool produces an address like `02:F3:A1:9C:4D:12` with the U/L bit set (bit 1 = 1), indicating a locally administered address. This is the same pattern Docker uses for container interfaces.
Recognizing a multicast address
Paste `01:00:5E:7F:00:01` into the tool. The I/G bit (bit 0) is 1, so the Transmission field shows Multicast. This address falls in the IPv4 multicast MAC range defined in RFC 1112, where the first 25 bits are `01:00:5E` followed by 0 and the lower 23 bits of the IP multicast group address.
Comparison with similar methods
| Method | Complexity | Typical use |
|---|---|---|
| UAA (Universally Administered) | OUI assigned by IEEE, globally unique | Physical network interfaces (NICs) |
| LAA (Locally Administered) | U/L bit set, organization-assigned | VMs, containers, test environments |
| Multicast MAC | I/G bit set, group destination | IPv4/IPv6 multicast, broadcast protocols |
| Random with vendor OUI | Real OUI prefix, random suffix | Testing with realistic-looking addresses |
| Random LAA | U/L bit set, I/G bit clear | Docker, Kubernetes pod interfaces |
Limitations or considerations
The built-in OUI database is a curated subset of common vendors. It does not contain every OUI from the IEEE registry. If the tool reports 'Unknown vendor', the OUI may still be valid but simply not in the included subset. Download the full OUI registry from the IEEE website for complete coverage.
The tool does not query the IEEE database in real time. It works offline using the embedded dictionary. For the most up-to-date vendor information, cross-reference with the live IEEE registry.
MAC address randomization (used by iOS, Android, and Windows for privacy) means that a device's MAC may change per network. The OUI of a randomized address will not match the actual device manufacturer if the U/L bit is set.
This tool does not perform ARP lookups, ping sweeps, or any network scanning. It is a pure lookup and generation utility.
Frequently asked questions
What is an OUI and how is it assigned?
OUI stands for Organizationally Unique Identifier. It is the first 24 bits of a MAC address, assigned by the IEEE Registration Authority. Organizations pay a fee to receive a block of OUIs, which they then use to assign unique MAC addresses to their network interfaces. The IEEE publishes the full registry at standards-oui.ieee.org.
What do the U/L and I/G bits mean?
Bit 1 of the first byte is the U/L (Universal/Local) bit. When 0, the address is universally administered (assigned by the manufacturer via their IEEE OUI). When 1, it is locally administered (set by the organization). Bit 0 is the I/G (Individual/Group) bit. When 0, the address is unicast (one device). When 1, it is multicast (a group of devices).
Why does my phone show a different MAC on each Wi-Fi network?
Modern operating systems (iOS 14+, Android 10+, Windows 10+) implement MAC randomization for privacy. They generate a new locally administered MAC address for each Wi-Fi network, preventing tracking across networks. These randomized addresses have the U/L bit set and will not match any vendor OUI.
Can two devices have the same MAC address?
On the same network segment, no. Duplicate MAC addresses cause ARP conflicts and packet loss. On different network segments, it is technically possible but should not happen with properly assigned UAAs. Locally administered addresses can collide if two organizations use the same range without coordination.
How does Docker assign MAC addresses to containers?
Docker generates MAC addresses with the U/L bit set (locally administered) and the I/G bit clear (unicast). The default bridge network uses the `02:42:xx:xx:xx:xx` range, where the last 4 bytes are derived from the container's IP address. This avoids collisions with real hardware MACs.
Conclusion
MAC address lookup is a quick way to identify device manufacturers on a network, and understanding the U/L and I/G bits helps distinguish physical hardware from virtual interfaces. This tool includes a curated OUI database and a random MAC generator for testing. For generating other types of unique identifiers, see the UUID Generator, Snowflake ID Generator, and NanoID Generator.