Which identifier is unique to each network interface on a local network?

The identifier that is unique to each network interface on a local network is the MAC address. A Media Access Control (MAC) address is a hardware address that serves as a unique identifier for network interfaces at the data link layer of a network. Each network interface card (NIC) is assigned a specific MAC address by its manufacturer, and no two devices should have the same MAC address on the same local network. This uniqueness allows devices on the same network to communicate effectively without confusion.

In contrast, while an IP address can uniquely identify a device on a specific network, it can change if the device moves to another network or if it is assigned a new address by a DHCP server. DNS addresses and Network IDs serve different purposes; DNS is used to resolve domain names to IP addresses, and a Network ID refers to a segment or domain within a network rather than a specific device.