What are hubs, switches and router?

Question

Network administration

Help to understand these devices. What are these devices, how do they work and how do they differ? Everywhere there is a very complicated description and there is really no detailed explanation of the principle of operation.

Answer 1

Listen here, grandfather will now try in a boyish way.
A hub is a "hub".
Most of all, it is similar in meaning to a crookedly made electric carrying tee, when several more are soldered to one outlet. It works like this: it stupidly sends everything that comes into any hole to all other holes. And the computers are already figuring out whether it's for me or not for me.
Now almost nowhere are they used anymore due to cheaper switches.
A switch is a "switch".
It is in spirit such an already normally made electric extension tee, quite usable.
It works like this: it reads the address in the header, to whom it came, and sends it only to the right hole.
There are different numbers of ports (holes) - from small desktop (4-8 ports) to large rack-mount (for example, 48 ports).
Both the hub and the switch are used to form networks - computers poke into them. You can also use both devices really as an extension cord when there are not enough "holes".
A router is a "router". (router).
A smart device with a processor and memory, already quite thinking. It is used to combine networks (as well as for separation, i.e. removal to a separate subnet). The main feature is that it keeps in memory the rules of how to get from network A to network B. Thus, it allows computers on one network to reach a computer on another network. This leaves two different networks.
Approximately as a telephone exchange - operates with the concepts of "internal call", "local call in the city", "intercity" and, depending on the dialed number, connects to the desired destination station. By the way, this is a good example, because modern PBXs have to solve purely router tasks of finding the shortest route, keeping the state of directions in memory, balancing the load, etc. Yes, and in telephony this is called "routing calls".
Another simple household example is any home routers. One network is LAN, everything that you have at home (everything that hangs on WiFi and is connected by wire), the other network is WAN, that is, the Internet from the provider. And your router just links these two networks.

Answer 2

Hubs and switches are layer 2 devices (OSI models), while the hub sends the received packet to all its ports, except for the one from which the packet came, and the switch tries to determine which of its ports is the layer 2 address (if we we are talking about Ethernet, then this is the MAC address) of the recipient and send the packet only there. Layer 2 devices can only connect the same channels.
The router is a layer 3 device. It can connect different layer 2 links (eg Ethernet and GPRS or PPP or MPLS). It "forgets" the sender's layer 2 address, extracts the layer 3 (IP) address from the packet, finds which of its channels the recipient's IP is most likely behind, and throws the packet into that channel (adding the required link layer address).