For example, this is a valid MAC address: D8-D3-85-EA-1B-EE. MAC addresses are usually written in the form of 12 hexadecimal digits. In the following picture we can see the structure of a MAC address: The manufacturer then assigns a unique value for the last 3 bytes, which ensures that every MAC address is globaly unique. Every network card manufacturer gets a universally unique 3-byte code called the Organizationally Unique Identifier (OUI). Manufacturers agree to give all NICs a MAC address that begins with the assigned OUI. MAC addresses are 6 Bytes (48 bits) long.
Every Ethernet network interface card (NIC) has a MAC address burned in its firmware, which is why MAC addresses are sometimes known as hardware addresses. Ethernet uses MAC (Media Access Control) addresses to uniquely identify a host in an Ethernet environment.