Switch

A switch is a network device whose main purpose is to facilitate communication within a network.

Switches operate at Layer 2 of the OSI model, which means they only see every gram of data up to the Layer 2 header. The Layer 2 header contains information that allows hop to hop delivery, such as the Source and Destination MAC addresses.

Switches operate by maintaining what is known as a MAC Address table. This is a table that maps the MAC addresses of devices connected to each switch port. A typical switch has a lot of ports, from 24 to 48, to 96, or more.

The MAC Address Table is filled in by looking at the Source MAC address field of each received frame.

To forward a frame, the Switch will look up the Destination MAC address in the MAC Address Table to determine what port to use.

If the Switch encounters a frame that does not know the location of the Destination MAC address, it simply duplicates and floods the frame out of every switch port (except the port it was received on).