MAC addresses

Every device connected to an Ethernet network has a unique MAC address , assigned by the manufacturer of the network card . Its function is like that of an IP address , since it serves as a unique identifier that enables devices to talk to each other . However , the scope of a MAC address is limited to a broadcast domain , which is defined as all the computers connected together by wires , hubs , switches , and bridges , but not crossing routers or Internet gateways . MAC addresses are never used directly on the Internet , and are not transmitted across routers .