Malcolm Rivera
A MAC address is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. The first three octets of a MAC address are known as the Organizationally Unique Identifier (OUI). The OUI is a 24-bit number that identifies a vendor, manufacturer, or other organization. OUIs are purchased from the Institute of Electrical and Electronics Engineers (IEEE) Registration Authority and are used to uniquely identify a particular piece of equipment. In this way, the OUI portion of a MAC address can be used to identify the manufacturer of a device.
| Characteristics | Values |
|---|---|
| OUI full form | Organizationally Unique Identifier |
| OUI bit size | 24-bit |
| OUI format | XX-XX-XX or XXXXXX |
| OUI in MAC address | First 3 octets of the MAC address |
| OUI assignment | Assigned by IEEE Registration Authority |
| OUI assignment to | Vendor, manufacturer, or organization |
| OUI representation | Set of octets separated by dashes or colons |
| OUI representation (other) | String of 5 or 6 bytes, or base 16 number |
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What You'll Learn
OUI is a 24-bit unique identifier for organisations, vendors or manufacturers
A MAC address is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. MAC addresses are used in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth.
The OUI (Organizationally Unique Identifier) is a 24-bit number that is a unique identifier for organisations, vendors or manufacturers. The OUI is the first 3 bytes of a MAC address, or the first 3 octets in transmission order. The OUI is purchased from the IEEE Registration Authority by the assignee (vendor, manufacturer or other organisation). The OUI is then combined with a 24-bit number assigned by the assignee to form the MAC address.
The OUI can be used to identify the manufacturer of a device. For example, if a device has a MAC address of A0:91:A2:01:02:03, the OUI is A0:91:A2, which belongs to OnePlus, a cell phone manufacturer. Therefore, it can be assumed that the device in question is a OnePlus cell phone.
The OUI can also be used to determine what devices are connected to a given Wi-Fi network, or even clients that are not connected but are nearby. Tools such as Aircrack-ng's airodump-ng allow users to passively observe the MAC addresses of Wi-Fi access points and their clients.
The OUI is also used in other contexts, such as in the SNAP protocol, where it serves as a company identifier.
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OUI is combined with a 24-bit number to form the MAC address
An Organizationally Unique Identifier (OUI) is a 24-bit number that identifies a vendor, manufacturer, or other organisation. OUIs are purchased from the Institute of Electrical and Electronics Engineers (IEEE) Registration Authority by the assignee. In MAC addresses, the OUI is combined with a 24-bit number (assigned by the assignee of the OUI) to form the address. The first three octets of the address are the OUI.
The MAC address consists of 6 octets. The first 3 octets of the MAC address are the OUI. For example, if we have a random MAC address of A0:91:A2:01:02:03, the OUI would be A0:91:A2. The OUI can help get a picture of the devices on the network by using the publicly available IEEE registration information related to it.
The EUI-48 is an identifier that is formed by concatenating the 24-bit OUI with a 24-bit extension identifier that is assigned by the organisation that purchased the OUI. The resulting identifier is generally represented as a set of octets separated by dashes (hexadecimal notation) or colons (bit-reversed notation) as in FF-FF-FF-FF-FF-FF or FF:FF:FF:FF:FF:FF, or as a string of 6 bytes as in {FF,FF,FF,FF,FF,FF}.
The CDI-40 was historically recommended as a context-dependent identifier that was formed by concatenating the 24-bit OUI with a 16-bit extension or by concatenating a 36-bit OUI-36 with a 4-bit extension. The extension was assigned by the organisation that purchased the OUI. The resulting identifier was generally represented as a set of octets separated by dashes (hexadecimal notation) or colons (bit-reversed notation) as in FF-FF-FF-FF-FF or FF:FF:FF:FF:FF, as a string of 5 bytes as in {FF,FF,FF,FF,FF}, or as a base 16 number as in FFFFFFFFFF16.
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The first three octets of the MAC address are the OUI
A MAC address, or Media Access Control address, is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. This is commonly used in IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth.
The OUI can be used to identify the manufacturer of a device. For example, if a device has the MAC address A0:91:A2:01:02:03, the OUI is A0:91:A2, which belongs to OnePlus, a cell phone manufacturer. Therefore, it can be assumed that the device is a OnePlus cell phone.
The OUI is also used in other standards and protocols, such as the SNAP protocol, where it serves as a company identifier. Additionally, the OUI can be used to look up publicly available IEEE registration information to get a picture of the devices on a network.
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OUI is used to identify the manufacturer of a device
An Organizationally Unique Identifier (OUI) is a 24-bit number that helps identify a vendor, manufacturer, or other organisation. OUIs are purchased from the Institute of Electrical and Electronics Engineers (IEEE) Registration Authority and are used to uniquely identify a particular piece of equipment. In the context of MAC addresses, the OUI is the first three octets of the address and is combined with a 24-bit number assigned by the assignee of the OUI.
The OUI is an essential component of a MAC address, which is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within a network segment. MAC addresses are used in various networking technologies, including Ethernet, Wi-Fi, and Bluetooth, and are typically represented as six groups of two hexadecimal digits, separated by hyphens, colons, or no separator.
By using the publicly available IEEE registration information, the OUI can help identify the manufacturer of a device. For example, if a device has the MAC address A0:91:A2:01:02:03, the OUI is A0:91:A2. By looking up this OUI, we can determine that it belongs to OnePlus, a cell phone manufacturer. Therefore, we can assume that the device in question is a OnePlus cell phone.
It is important to note that while the OUI can provide valuable information about the manufacturer of a device, it should be used cautiously as it may not always be accurate or up-to-date. Additionally, MAC addresses are primarily used for local network communication and do not inherently contain location information, making it challenging to track a device's location based solely on its MAC address.
There are various tools available, such as online lookup tools and software like Wireshark and Nmap, that can assist in determining the manufacturer of a device based on its MAC address or OUI. These tools utilise databases that contain MAC addresses and their associated vendors, making it easier to identify the manufacturer of a device.
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OUI is purchased from the IEEE Registration Authority
Organizationally Unique Identifiers (OUIs) are 24-bit numbers that uniquely identify vendors, manufacturers, or other organisations. They are purchased from the IEEE Registration Authority by the assignee (the IEEE term for the vendor, manufacturer, or other organisations). OUIs are used to identify a particular piece of equipment through derived identifiers such as MAC addresses, Subnetwork Access Protocol protocol identifiers, World Wide Names for Fibre Channel devices, or vendor blocks in EDID.
The IEEE Registration Authority is the administrative body responsible for registering and administering OUIs and other identifiers used in the computer and electronics industries. It was formed in 1986 in response to a need for this service, which was recognised by the P802 (LAN/MAN) standards group. The IEEE Registration Authority is currently recognised by ISO/IEC as the authorised registration body to provide the service of globally assigning, administering, and registering OUIs.
The IEEE Registration Authority assigns these unique identifiers to companies that need to include them in a product with networking capability. In MAC addresses, the OUI is combined with a 24-bit number (assigned by the assignee of the OUI) to form the address. The first three octets of the address are the OUI. The OUI can help get a picture of the devices on the network by using the publicly available IEEE registration information related to it.
The IEEE Registration Authority also handles other identifiers, such as Individual Address Blocks (IABs), Manufacturer IDs, Standard Group MAC Addresses, Unique Registration Numbers (URNs), and EtherType values. The prices for the various assignments available from the IEEE Registration Authority may be found on the IEEE RA website for each registry.
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Frequently asked questions
OUI stands for Organizationally Unique Identifier. It is a 24-bit number that uniquely identifies a vendor, manufacturer, or organization.
The OUI is the first three octets of a MAC address. The OUI is combined with a 24-bit number assigned by the assignee of the OUI to form the MAC address.
A MAC address consists of six groups of two hexadecimal digits, separated by hyphens, colons, or no separator. The first three sets of two hexadecimal numbers are the OUI. For example, in the MAC address "A0:91:A2:01:02:03", the OUI is "A0:91:A2".
You can use an online MAC address lookup tool. Enter the MAC address, and the tool will provide the vendor name.
