All network operations depend on a hierarchy of addresses in order to enable the network’s devices to exchange information. The most basic address in networking operations is the Media Access Control address (MAC address) that serves as a unique identifier for every device attached to a network. These addresses are typically assigned to the devices by their manufacturers and stored in their firmware.
The standard 48-bit format for generating a MAC address specifies six pairs of hexadecimal digits. For display purposes, the number is written as six number pairs separated by hyphens (-) or colons (:)—for example,
This original 48-bit format is known as the EUI-48 (Extended Unique Identifier) in IEEE terms. This format corresponds to the original Ethernet IPv4 addressing scheme for networking and is used in wireless 802.11 and Bluetooth networking technologies.
The EUI-64 bit version of the MAC address code enlarges the code to eight pairs of hexadecimal digits. For example, a given device could be assigned the MAC address = 00:13:A2:00:40:6B:8E:66. This format corresponds to the IPv6 addressing scheme and is included in Firewire, ZigBee, and 802.15 technologies.
MAC addressing is associated with OSI Layer 2 operations. This layer is responsible for establishing the logical access and connectivity to and from each network port. Different network connectivity devices, such as switches and routers, rely on MAC addresses as the basis for building and using internal content addressable memory (CAM) tables. The devices use these tables to route messages they receive from one network segment to a location on another network segment based on the hardware port to which the intended recipient is connected.
Many connectivity devices build and maintain their CAM tables through a MAC learning and discovery process. As they interact with devices connected to their physical ports, they read message headers to acquire the sending and receiving devices’ MAC addresses and record them in the CAM along with their port information.