There are three network devices commonly found in today’s LANs , namely: hubs, switches and routers.
Hubs
A hub serves as a central point to which all of the hosts in a network connect to. A Hub is an OSI Layer 1 device and has no concept of Ethernet frames or addressing. It simply receives a signal from one port and sends it out to all other ports. Here is an example 4-port Ethernet hub (source: Wikipedia)
Today, hubs are obsolete and switches are more in use.
Switches
Like hubs, a switch is also one of the network devices that is used to connect multiple hosts together, but it has many advantages over a hub. Switch is an OSI Layer 2 device, which means that it can inspect received traffic and make forwarding decisions. Each port on a switch is a separate collision domain and can run in a full duplex mode (photo credit: Wikipedia).
Routers
A router is a device that routes packets from one network to another. A router is most commonly an OSI Layer 3 device. Routers also divide broadcast domains and have traffic filtering capabilities.
The picture below shows a typical home router:
In the next sections we will describe each of these network devices in more detail.