Network hardware

Network hardware

Wired network hardware. Approach to the theory of network design.

In this post we will talk about the features and services offered by the equipment used in the basic physical infrastructure that allows the operation of a network.

End user equipment

All communication network systems have a single purpose, allowing the connection between personal computers, mobile phones, radio, web servers and much more. The network infrastructure makes no sense without the need to send information from one computer to another, in different places.

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The end user equipment within a communications network must use the same protocols and appropriate hardware for the physical channel implemented, for example in the case of an office a computer must have a network card if access is via cable or Wifi antenna if network access is wireless. Communications are not necessarily between computers, they can be between radio equipment or cell phone. What is common to all these end devices is that each one has implemented all the necessary standard network protocols to guarantee communication between them.

Although protocols and security configurations implement measures to detect and/or block terminals that send malformed information, either voluntarily or by mistake, a network administrator monitors the network to prevent a malfunction from affecting the integrity of the data of the rest of users.

Hubs

It was born to cover the need to reduce the number of cables necessary for the assembly of a network. Until that time, a new independent network cable had to be placed for each connection. The concentrators allowed connection to different nearby equipment using a single output cable. Thus, if a new device was added to the network in the same room, you only had to pull a cable to the hub so that you had access to the network.

It works in the physical layer (layer 1) on the OSI model, or the access layer on the TCP/IP model. When a hub receives a signal through an interface, it simply repeats it through all its interfaces, except for the one where the broadcast came in. All connected equipment receives the communications that go through it, so everyone knows if the channel is free and whether or not they can send information. Although at the time of the creation of this system there was no special interest in confidentiality, it is clear that it is a system that allows you to control all the communications that pass through that computer.

Since each packet is sent through any other port, collisions appear that prevent traffic flow. Due to these problems, the concept of hub evolved to that of switch.

Switches

It is a logical digital device that interconnects two or more hosts intelligently. It operates in the data link layer of the OSI model. If the device knows by which interface the recipient of the information “listens”, it only sends the traffic through that mouth. This reduces traffic and minimizes collisions, achieving greater efficiency. The appearance of the switches allowed the creation of large local area networks and greatly facilitated the implementation in corporate environments.

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It is a device that allows us to save on cabling, and with the appearance of network status protocols such as “Spanning Tree Protocol”, or simply STP, the creation of redundant network structures that eliminated the possibility of that the failure of a single device implied the loss of the entire network.

Automatic learning

Suppose we have a new device newly connected to our network. At this time, the switch knows nothing about the network. When you receive the first message from a computer, write down the MAC address of the sender in your address table and associate it with the physical interface through which you received the traffic.

When you check the destination MAC address, check that you don’t have it in your table. Remember that we have just connected it to the network and it has no information, therefore, it will send that data packet through all its network interfaces. So far he is working as a hub, but it is only the initial process during which he is learning information from the network. After a while, when the receiver of the previous message decides to respond, the new traffic will arrive at a mouth of our switch. The device will write the new source MAC in its address table and check the destination MAC address. This time it does have that MAC registered, so it will send traffic only through that interface. Here it no longer works as a hub, but only sends it through those interested interfaces. With the passage of time, you will learn new assignments of MAC addresses and physical interfaces, making the network increasingly efficient. With this commuted traffic we improve the privacy of communications, since except in the moments that we do not have information, it does not forward traffic to equipment that is not interested in it.

One of the problems of the switches are the loops or routing Loop that occur because they detect that a device is accessible through two ports emit the frame by both, but of this I will write later so there is nothing to worry about.

Routers

Routers are network devices that work at layer 3 of the OSI model, or the Internet layer in the TCP/IP model. Its function is to send the data packets between the different networks to which they are directly connected and route the packets that go to remote networks in the best possible way. Its operation is based on the maintenance of a route table that allows you to send the information to your destination. There are dozens of routing protocols that allow these tables to be fed in such a way that it is easy to find the one that best suits the needs of the infrastructure. When routers encounter traffic whose destination is not in their tables, they forward that traffic to their default gateway in the hope that that team does know how to get the data to the destination. The switches opt for flooding, the routers simply have a last resort node in their table to send the information to if they don’t know where. One feature that we must take into account is that routers do not allow the forwarding of broadcast messages, so the local network information sent to the broadcast addresses does not leave the network itself. This is why it is often said that routers are delimiters of the collision domain.

Layer 3 switches: (intermediate network equipment)

A Layer 3 (or multilayer) switch combines some of the functions of a Switch (layer 2 OSI model) and those of a router (layer 3 of the OSI model).

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Thanks to the technological evolution, many functions can be delegated to the software that makes them work, this allows reducing costs, since no specific physical equipment is needed for each function and also, adding new functionalities that were previously reserved to other equipment, such as for example, the ability to create VLAN networks to separate different traffic flows within a local area network and security features that did not exist in traditional “switches”, such as the possibility of detecting and blocking other network equipment not authorized through the use of “access lists”.

Network bridges

A network bridge is the computer network interconnection device operating in layer 2 (data link level) of the OSI model; It allows connection between computers without routers. It works through a table of MAC addresses detected in each segment to which it is connected. When it detects that a node of one of the segments is trying to transmit data to a node of the other segment, the bridge copies the frame for the other network segment, having the ability to filter the frame in case of not having said network segment as destination.

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To know where to send each frame that arrives, it includes a machine learning mechanism so they do not need manual configuration. We will see this in more detail when we address the issue of routing.

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