Layer 2 Devices

Bridges have two ports and connect two independent PHYSICAL networks. These days, you are most likely to encounter a bridge in virtualization software or a system's network interfaces. (e.g. bridging vs NAT mode for VMs, or combining two interfaces in Linux )

Switches are multiport bridges and are still prevalent networks today. Switches are typically the lowest level device that makes decisions on where to send traffic. The MAC (Media Access Control) address is what switches use to make those decisions.

• Multiple Collision Domain

  (Each physical connection to a switch port is a collision domain)

• Single Broadcast Domain