A network-switch is a device that filters and forwards packets between segments.
Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3)
of the OSI Reference Model and therefore support any packet protocol.
LANs that use switches to join segments are called switched LANs or, in the case of Ethernet networks,
switched Ethernet LANs.
A LAN switch creates a series of instant networks that contain only the two devices communicating
with each other at that particular moment.
In a fully switched network, switches replace all the hubs of an Ethernet
network with a dedicated segment for every node. These segments connect to a
switch, which supports multiple dedicated segments (sometimes in the hundreds).
Since the only devices on each segment are the switch and the node, the switch picks
up every transmission before it reaches another node.
The switch then forwards the frame over the appropriate segment. Since any
segment contains only a single node, the frame only reaches the intended
recipient. This allows many conversations to occur simultaneously on a
switched network. This is of course also a much safer environment then with hubs.