Switch

A switch is a network device responsible for sending network traffic to an intended host. Unlike hubs, switches keep track of what other network devices (via MAC addresses) it has "seen," and associates this with the relevant port.

Switches are usually superior to hubs for three reasons:

1. Performance. A good switch can route seperate streams of traffic to different ports simultaneously. For example, given 4 computers (A, B, C, and D), with two connections (A talks to B, and C talks to D), the two streams will not interfere with eachother. This aggregate bandwidth is sometimes called the "fabric bandwidth."
2. Security. Since traffic is sent only to ports that have "interested" hosts, a device on a different port cannot easily eavesdrop on the network traffic in which it is not directly involved (because the switch knows that shouldn't listen!).
3. Administration. Switches also offer a number of other administration features, such as vlan support, tracking performance and traffic metrics (often via SNMP or rmon), per-port and per-host authentication to provide additional network security. Many switches can also act as NTP servers, providing a central location for time services in a network.