Media Access Control Address
lastmod 2022-10-07created 2017-11-302 edits
A MAC address (Media Access Control Address) is a unique identifier assigned to a network interface for communication at the data link layer of a network segment.
MAC addresses are used as network addresses in most IEEE 802 network technologies, including Ethernet and Wi-Fi. Logically, MAC addresses are used in the medium access control protocol sublayer of the OSI model.
MAC addresses are usually assigned by the manufacturer of the network interface controller (NIC) and stored in its hardware, such as the card's read-only memory or some other firmware mechanism. When assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be called a BIA (burned-in address). It is also called an Ethernet hardware address (EHA), hardware address, or physical address (not to be confused with a physical memory address). This differs from a programmed address, where the host device issues commands to the NIC to use an arbitrary address.
A single network node can have multiple NICs, and each NIC has its own unique MAC address. Complex network equipment such as multilayer switches and routers may require one or more permanently assigned MAC addresses.
MAC addresses are formed according to the rules of one of three namespaces managed by the Institute of Electrical and Electronics Engineers (IEEE): MAC-48, EUI-48, and EUI-64. The IEEE holds trademarks on the names EUI-48 and EUI-64, where EUI stands for Extended Unique Identifier.
- Except for locally administered MAC addresses, ordinary MAC addresses carry a number unique to each equipment vendor, so this information can also be used to identify the manufacturer of the hardware.
- A standard MAC address following the rules set by the IEEE consists of 48 bits in total. The first 24 bits are the OUI (Organizational Unique Identifier), the manufacturer's identification code, which identifies the NIC manufacturer; the remaining 24 bits hold information about that vendor's LAN card.
- Of the 6 bytes (48 bits) of a MAC address, the first 3 bytes (24 bits) are a unique code assigned to each vendor, so the vendor can be identified from the MAC alone. You can look it up on the IEEE MAC address management page by entering the upper 3 bytes (24 bits) and clicking Search.