Читать книгу Networking All-in-One For Dummies - Lowe Doug, Doug Lowe - Страница 41

A switch is a layer-2 device that is similar to a hub in that it allows you to connect more than one device, and packets received on one port are relayed to other ports. The difference, however, is that a switch is able to examine the actual contents of the data that it receives. As I explain in the “Pondering Packets” section, later in this chapter, data is sent in units called packets that contain a destination address. A switch looks at this destination address and repeats the incoming packet only on the port that can deliver the packet to the intended destination.

For example, suppose Computer A is connected to switch port 1, and Computer D is connected to switch port 4. If Computer A sends a packet to Computer D, that packet is received on switch port 1. The switch knows that Computer D is connected to switch port 4, so the switch sends the packet out on switch port 4. In this way, Computer D receives the packet. The computers or devices that are connected to the other ports on the switch are not bothered with the packet intended for Computer D.

If that doesn’t make a lot of sense, don’t worry: It will. The next two sections in this chapter explain the concept of MAC addresses, which are how networks identify the intended recipients of data packets, as well as how data packets work. Then, in Chapter 3 of this minibook, I dive deeper into how switches do their magic.