Switch - A Layer 2 Network device

In computer network, Switch is a layer two device. This layer 2 is taken from OSI model where layer two represented as Data link layer. We will talk about OSI Model in another blogs. In old bridges software is used to create and manage a Content Addressable Memory filter table while new switches use application-specific integrated circuits (ASICs) to build and maintain their MAC filter tables. Layer 2 Switches and bridges are faster than routers because they don't take up time looking at the Network layer header information. Instead, they look at the frame's header before deciding to forward, flood, or drop the frame.

Advantages of having Layer 2 Switch -

Hardware-based bridging (ASICs)
Wire Speed
Low Latency
Low cost

Switch Function at Layer 2

MAC address Learning : Layer 2 Switch remember source hardware address of each frame received on an interface and enter this information into a MAC database called a forward/filter or CAM table.

Forwarding/Filtering : When a frame is received on an interface, the switch looks at the destination mac address to choose appropriate exit interface in its CAM table.

Loop avoidance : If we have multiple connections between switches for redundancy purpose, It may cause for a layer 2 loop in the network. To avoid this layer 2 loop in the network Switches use STP (spanning tree protocol) and prevent a loop in network while still allowing the redundancy.

How to check Switch MAC address table -

In cisco switches we have very simple command to check the MAC addresses on a switch interfaces.