Which identifier uniquely identifies a network interface at the hardware level?

• A. MAC address
• B. IP address
• C. Hostname
• D. Domain name

Answer: (A)

MAC addresses are the hardware identifier assigned to a network interface card. They’re designed to be unique for each NIC and are usually 48 bits long, shown as six hexadecimal octets. This address is used by devices on the local network to deliver frames at the data link layer, and it remains tied to the physical interface regardless of how IP addressing or names are configured. In contrast, an IP address is a software-side, routable address at the network layer and can change with networks, while hostnames and domain names are human-friendly labels resolved by DNS and don’t identify the hardware itself.