A hub (sometimes called a repeater) is a layer 2 networking device, similar to a switch, but not as advanced. Instead of sending a datagram to a specific ethernet address, the hub
will simply forward the datagram to every port, except for
the one it came from. They are common in
small networks, but the massive overhead caused by all the datagrams being sent to every device on the network makes them extremely impractical in large networks. They are becoming less common as
time passes on. However, they are immune to looped cabling in the network, but more and more switches are equipped with the Spanning Tree Protocol, which prevents against
issues with looped connections. Wiring the network correctly also helps with this.