Network Addressing
Network addressing identifies either individual devices or groups of devices on a LAN. A pair of network devices that transmit frames between each other use a source and destination address field to identify each other. These addresses are called unicast addresses, or individual addresses, because they identify an individual network interface card (NIC).
The IEEE defines the format and assignment of network addresses by requiring manufacturers to encode globally unique unicast Media Access Control (MAC) addresses on all NICs. The first half of the MAC address identifies the manufacturer of the card and is called the organizationally unique identifier (OUI).