Network switches

A switch is a device that performs switching. Specifically, it
forwards and filters OSI layer 2 datagrams (chunk of data
communication) between ports (connected cables) based on the
Mac-Addresses in the packets.This is distinct from a hub in that it
only forwards the datagrams to the ports involved in the
communications rather than all ports connected. Strictly speaking, a
switch is not capable of routing traffic based on IP address (layer 3)
which is necessary for communicating between network segments or
within a large or complex LAN. Some switches are capable of routing
based on IP addresses but are still called switches as a marketing
term. A switch normally has numerous ports with the intention that
most or all of the network be connected directly to a switch, or
another switch that is in turn connected to a switch.

Switches is a marketing term that encompasses routers and bridges, as
well as devices that may distribute traffic on load or by application
content (e.g., a Web URL identifier). Switches may operate at one or
more OSI layers, including physical, data link, network, or transport
(i.e., end-to-end). A device that operates simultaneously at more than
one of these layers is called a multilayer switch.

Overemphasizing the ill-defined term "switch" often leads to confusion
when first trying to understand networking. Many experienced network
designers and operators recommend starting with the logic of devices
dealing with only one protocol level, not all of which are covered by
OSI. Multilayer device selection is an advanced topic that may lead to
selecting particular implementations, but multilayer switching is
simply not a real-world design concept.