A switch is a device that operates at layer 2 of the OSI stack, and is the most common device that you would find in the network.
Many layer 2 technologies came into existence at different times, to meet user requirements. Some of these layer 2 technologies are X.25, Frame Relay, ATM, and Ethernet. There are switches available for each of these technologies.
Out of the multiple layer 2 competing technologies, Ethernet became the de facto standard at layer 2 of the OSI model, primarily driven by its low cost and the fact that Ethernet scales from 10 Mbps to 40 Gbps and beyond. This book will use the term switch in general for an Ethernet switch.
A typical model of a Cisco catalyst switch with Ethernet ports is shown in the following ...