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 use is common in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth. Within the Open Systems Interconnection (OSI) network model, MAC addresses are used in the medium access control protocol sublayer of the data link layer. As typically represented, MAC addresses are recognizable as six groups of two hexadecimal digits, separated by hyphens, colons, or without a separator.

MAC addresses are primarily assigned by device manufacturers, and are therefore often referred to as the burned-in address, or as an Ethernet hardware address, hardware address, or physical address. Each address can be stored in hardware, such as the card's read-only memory, or by a firmware mechanism. Many network interfaces, however, support changing their MAC address. The address typically includes a manufacturer's organizationally unique identifier (OUI).

MAC addresses are used for a variety of purposes, including:

* Identifying devices on a network
* Controlling access to a network
* Troubleshooting network problems
* Blocking unwanted traffic
* Tracking devices

MAC addresses are not routable on the Internet, but they can be used to identify devices that are connected to the Internet. This information can be used by network administrators to track down sources of malicious traffic or to block unauthorized devices from accessing the network.

Here are some examples of how MAC addresses are used:

* A wireless router can use MAC addresses to control access to the network. For example, a router can be configured to only allow devices with specific MAC addresses to connect to the network.
* A firewall can use MAC addresses to block unwanted traffic. For example, a firewall can be configured to block all traffic from devices with specific MAC addresses.
* A network administrator can use MAC addresses to track devices on a network. For example, an administrator can use MAC addresses to see which devices are connected to the network and where they are located.

MAC addresses are a valuable tool for network administrators and security professionals. By understanding how MAC addresses work, you can better understand how your network operates and how to protect it from unauthorized access.
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