First let us discuss about the HUBs, HUB is a dumb device, which does not have any intelligence and is considered as Layer 1 device.
HUB has no other functionality other than forwarding frames, whenever it receives a frame, it does not know whom to deliver the frame, because it has no intelligence, so it forwards the Frames out to all ports, regardless of who actually needs the frame, which is a biggest disadvantage if used in an environment where hundreds of hosts are connected and working simultaneously. It really slows the speed of data transfer in the network.
There is one more Layer 1 device, known as Repeater, which we can think of an extension board.
Works in a Half-Duplex mode.
Switches:
After HUB, when use of network increased rapidly, people needed something which would not be slow if used in a large network environment, hence came the Layer 2 device, The Bridge which had its own intelligence and used to make decisions based on Layer 2 address.
Besides forwarding frames, it uses its intelligence to learn all the devices connected to it and store them in a CAM table, that is, it learns the Physical Address of the devices, so that frames are forwarded to exactly the devices meant for.
Bridges uses Software to create and manage filter table.
Later, Bridges were upgraded to Switches, which were not software based, but used ASIC (Application Specific Integrated Circuits).
Switches and Bridges are almost similar, we can say that a Switch is a multiport bridge, Switches comes with more ports and it uses ASIC.
Other than that, work of Bridge and Switch are similar.
Switches and Bridges breaks up Collision Domain, each port is a separate Domain but still it is a one large Broadcast Domain.
Works in a Full-Duplex Mode.
Routers:
Switches and Bridges solved the problem of transferring data in a network segment, now we needed a device which could transfer data between different network segments, hence Routers came to the rescue, which is also an intelligent device, it had its own brain, and makes decision based on Layer 3 address, and hence it is also known as Layer 3 device.
Routers switches packets between network segments, it uses its intelligence to know about the networks connected to it directly or indirectly, and maintains a table known as a Route Table, and makes forwarding
decision based on the Route Table.
Router breaks up Broadcast domain, Routers do no propagate broadcasts. Each interface of a Router is a separate Broadcast Domain.
Works in a Full-Duplex Mode.
