A hub is used to connect devices so that they are on one LAN, as shown in Figure C-2. The cables normally used for Ethernet have RJ-45 connectors. Because only two devices can be connected with these cables, we need a hub if we want to interconnect more than two devices on one LAN.

Figure C-2 A Hub Connects Devices So that They Are on One LAN

A hub is not a "smart" device. A hub sends all the data from a device on one port to all the other ports. When devices are connected via a hub, the devices all hear everything that the other devices send, whether it was meant for them or not. This is analogous to being in a room with lots of peopleā€”if you speak, everyone will hear you. If more than one person speaks at a time, there will just be noise. Rules must be put in place if real conversations are to happen; in networking, these rules are the protocols.

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