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MAC addresses are generally permanent and hard-coded onto a device, representing a unique identifier for a network interface controller (NIC) at the data link layer of the OSI model. This means that each device on a network has a distinct MAC address assigned by the manufacturer, which is used for communication over a local area network. This characteristic ensures that devices can reliably identify one another within the same network segment.

Unlike IP addresses, which can change as devices move between networks or are reconfigured, MAC addresses remain constant for the lifetime of the network interface they are associated with. This stability is crucial for local network communications, particularly within Ethernet networks, as it allows switches and other networking hardware to accurately direct traffic to the correct device.