What is a network hub?

A network hub serves as a connection point for all devices in a LAN. It is basically a multiple-port repeater because it repeats an electrical signal that comes in one port out all other ports (except the incoming port). Here is an example 4-port Ethernet hub (source: Wikipedia):

ethernet hub

Hubs are OSI Layer 1 devices and have no concept of Ethernet frames or addressing. They have no way of distinguishing which port a signal should be sent to; instead, an electrical signal is broadcast to every port. All nodes on the network will receive data, and the data will eventually reach the correct destination, but with a lot of unnecessary network traffic:

how hub works

In the picture above you can see that the hub has sent out the receiving signal out all other ports, except the incoming port. 

Modern LANs rarely use hubs; switches are used instead. Hubs have many disadvantages, including:

  • they operate in half-duplex.
  • they are prone to collisions.
  • each port on a hub is in the same collision domain.
  • data is forwarded out all ports and can be captured with a network sniffer.
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