10/05/2020
Hubs, Bridges, Switches and Routers are used to build networks. If you are trying to design your own LAN (Local Area Network) at home, then you probably need to know what they do and the main differences between them. I will try to cover all that in addition to some networking details to cultivate the article and provide better understanding of how the internet works. After all, always remember that the internet as you know it is nothing more than a network of networks!
Hubs are used to build a LAN by connecting different computers in a star/hierarchal network topology, the most common type on LANs now a day. A hub is a very simple (or dumb) device, once it gets bits of data sent from computer A to B, it does not check the destination, instead, it forwards that signal to all other computers (B, C, D…) within the network. B will then pick it up while other nodes discard it. This amplifies that the traffic is shared.
There are mainly two types of hubs:
1. Passive: The signal is forwarded as it is (so it doesn’t need power supply).
2. Active: The signal is amplified, so they work as repeaters. In fact they have been called multiport repeaters. (use power supply)
Hubs can be connected to other hubs using an uplink port to extend the network.
OSI Model: Hubs work on the physical layer (lowest layer). That’s the reason they can’t deal with addressing or data filtering.
Switches on the other hand are more advanced. Instead of broadcasting the frames everywhere, a switch actually checks for the destination MAC address and forward it to the relevant port to reach that computer only. This way, switches reduce traffic and divide the collision domain into segments, this is very sufficient for busy LANs and it also protects frames from being sniffed by other computers sharing the same segment.
They build a table of which MAC address belongs to which segment. If a destination MAC address is not in the table it forwards to all segments except the source segment. If the destination is same as the source, frame is discarded.
Switches have built-in hardware chips solely designed to perform switching capabilities, therefore they are fast and come with many ports. Sometimes they are referred to as intelligent bridges or multiport bridges.
Different speed levels are supported. They can be 10 Mb/s, 100 Mb/s, 1 Gb/s or more.
Most common switching methods are:
1. Cut-through: Directly forward what the switch gets.
2. Store and forward: receive the full frame before retransmitting it.
OSI: Switches are on the data link layer (just above physical layer) that’s why they deal with frames instead of bits and filter them based on MAC addresses. Switches are known to be used for their filtering capabilities.
VLANs (Virtual LANs) and broadcast domains: Switches do not control broadcast domains by default, however, if a VLAN is configured in a switch it will has its own broadcast domain.
*VLAN is a logical group of network devices located on different LAN physical segments. However they are logically treated as if they were located on a single segment.
