MAC addressing (Media Access Control addressing) is a method used to uniquely identify network devices at the data link layer of the networking protocol stack. MAC addresses are assigned to network interface cards (NICs) and are used for communication within a local network.
MAC addressing plays a crucial role in local network communication, as it enables devices to identify and communicate with each other at the data link layer. By using MAC addresses, devices can exchange data within the same network without needing to know the IP addresses or higher-level protocols.
Key points
Uniqueness: MAC addresses are assigned by the manufacturer of the network interface card and are meant to be globally unique. Each NIC is assigned a unique MAC address, ensuring that no two devices on the same network have the same address.
Address Format: MAC addresses are 48 bits (6 bytes) in length and are usually represented in hexadecimal format. They are typically written in groups of two hexadecimal digits separated by colons or hyphens. For example, 00:1A:2B:3C:4D:5E.
Address Structure: A MAC address is divided into two parts: the Organizationally Unique Identifier (OUI) and the device-specific identifier. The first 24 bits (first three bytes) of the MAC address represent the OUI, which is assigned to the manufacturer by the Institute of Electrical and Electronics Engineers (IEEE). The remaining 24 bits (last three bytes) represent the device-specific identifier.
MAC addresses can be classified into three types.
Unicast Address: A unicast MAC address is assigned to a specific network device and is used for one-to-one communication.
Multicast Address: A multicast MAC address is used for one-to-many communication. Frames sent to a multicast address are received by multiple devices that have subscribed to that multicast group.
Broadcast Address: A broadcast MAC address is a special address (FF:FF:FF:FF:FF:FF) used to send frames to all devices on the same network.
MAC Address Learning
Switches and bridges in a network use MAC address learning to build a MAC address table, which associates MAC addresses with specific switch ports. This allows them to forward frames to the correct destination based on the MAC address in the frame’s header.
Limitations: MAC addresses are only significant within the local network or broadcast domain. They are not routable across different networks like IP addresses. When data needs to be sent to a device on a different network, IP addressing is used.