What does the MAC address do?
The MAC Address provides a way to distinguish one NIC from any other NIC.
Operations at the lower layers of the OSI model (the physical and data-link layers) do not directly recognize computer names or protocol addresses (e.g., the IP address). The MAC address allows a card to recognize the data that is sent to it. A NIC checks each frame or packet on the network traffic to see if it contains its MAC address. Once the NIC identifies a frame with its MAC address, it decodes the frame and processes it.
A bridge, which operates at the data-link layer, looks at MAC addresses. A router, which operates at the network layer, looks at protocol addresses. Thus, a router is able to perform more sophisticated traffic management functions than a bridge.