#WHAT_IS_COMPUTER_NETWORKING ?

A network is a set of computers connected to each other that can share information, (documents, images, etc), resources (printers, hard drives) and services. A network can be consisting of two computers or even having thousands of computers distributed all over the world (like the Internet).

Types of networks:

According to its size or coverage area:

Local Area Networks (LAN): small extension networks, as in a home, an institute, a university or a company.

Metropolitan Area Networks (MAN): Cover a larger area like a city or a municipality.

Wide Area Networks (WAN): connect computers between cities, countries or different continents.

According to your level of access or privacy:

Internet: It is a worldwide network of computer networks. It has public access. 
Intranet: It is a local network that uses Internet tools (web, mail, FTP, etc). It can consider as a private Internet that works within the same institution. 
Extranet: It is a virtual private network; is part of the Intranet of an organization that extends to users outside of it.

According to its functional relationship:

Client-server: Clients use the shared resources and services they provide
servers: web, data, print, etc.
Peer-to-peer (P2P) networks: All devices can act as clients or
servers.

According to its topology

Basic networking concepts:

Communication: It is the process that takes a message from a sender through a channel to a
receiver. In a network, computers are transmitters and receivers at the same time. The channel is the
means by which the data circulates: cables, fiber, etc. 

Protocol: It is the language and the set of rules by which the sender and receiver communicate. Internet protocol is the most used: TCP / IP

Private IP Address: Identifies each device on the network. It consists of 4 numbers
separated by points, with values from 0 to 255. The IP of a computer does not transcend on the Internet, since that it is the router through its external IP that is identified in the requests.

Public IP Address: Public IP is the IP address that is visible from the Internet. It is usually the one with the router or modem. It is the one that gives "the face" to the Internet. This IP is usually provided by the ISP (a company that gives you internet access: Cable One, AT&T Internet Services, etc.).

Gateway: It is the IP address through which the local network goes abroad, either another network or
Internet. It is usually the IP of the router (192.168.1.1). It is the same for all teams that share the router.

Netmask: Resembles the IP address, but determines what part of the IP address specifies the team and what part of the subnet it belongs to. It is used to create subnets. The most common mask in small networks is 255.255.255.0 and it indicates that the first three 8-bit packets from the IP are intended to identify the network and only the fourth to identify the equipment so it offers us a theoretical maximum of 253 connectable devices since 0 is the network identifier address, 1 is the default for the router and 255 for broadcast, so these values can no longer be used.

Workgroup: Computers are grouped into subnets for ease of use. For the ones
Computers on the same network can communicate must be in the same workgroup.

DNS (Domain Name System):  IP addresses are difficult to remember. Thus DNS is used to translate IP addresses into easy names for us (Ex:www.google.es). The default DNS servers used are those provided by the ISP with the one that contracts the service (Movistar, Vodafone, etc). There are also free DNS like the new ones Free DNS of Google 8.8.8.8 and 8.8.8.4 that can replace the DNS of our providers in the case of having navigation problems.

Network card: It is a hardware element whose function is to send and receive information to the rest
of the computers. It can be integrated into the motherboard or connected in a slot expansion. Each card has a unique identifier called a mac address, it consists of a 6-byte (48-bit) hexadecimal identifier. The first 3 bytes, called OUI, indicate the manufacturer and the other 3 serve to differentiate the cards produced by it. For example: 00-80-5A-39- 0F-DE.

Port: Interface to communicate with a program through the network. Example: HTTP service
uses port 80.

Interconnection devises:

Network cards :
They are the devices through which information is sent between the network and the computer. We have the following types:

PCI to cable (Ethernet). It connects to the motherboard.
Wireless PCI. It connects to the motherboard.
Wireless USB. Connects via USB.
Wireless MiniPCI. For laptops.

Routers:

They are devices that connect different networks of computers. For example a LAN network with
Internet. We have the following types:

Router with cables.
Wireless router.
Modem-USB.

Network cables:

They connect network devices to each other by a wire. They are the physical channel through which
transmit the data. They may be:
Coaxial cable: It is similar to that of the television antenna. It connects with the BNC connector.
Twisted pair: It is similar to the telephone cable. It consists of 8 braided conductive wires. There are
various categories (cat5e, cat6, cat6e). Connects with an RJ-45 type connector.
Optical fiber: The information is sent in the form of a light beam at a high speed.

Devices to communicate several computers on the same network with each other:

Hub. The information it receives is sent to all ports.
Switch. The information it receives is only sent to the port of the destination device.
Access point. It works just like a switch but sends the information over wifi.

Web server:

A web server is a program that runs continuously on a computer, keeping waiting for execution requests from a client or an Internet user. The server the web is responsible for answering these requests appropriately, delivering, as a result, a web page or information of all kinds according to the requested commands. At this point it is necessary to clarify the following: while the word server is commonly used to refer to a computer with server software installed, strictly speaking, the server is the software that allows the performance of the described functions.

The server would become the "home" (host or accommodation) of the sites we visit on the Internet.

The sites are hosted on computers with installed servers, and when a user visits them they are these computers that provide the user with interaction with the site in question. When a web hosting plan is contracted with a company, the latter provides a server to site owner to host it; there are two options, choose a "server dedicated ", which refers to a server computer dedicated exclusively to the site of the

client (for high demand applications), or a "shared server", which means that a same server (served computer + program) will be used for multiple clients sharing the resources.

Connecting an ADSL network

In the image, we see the way to connect the computers to a network with an Internet connection by

ADSL. We can see that the telephones on the line with ADSL must have microfilters to avoid interference when speaking.

Network settings in Windows:

1. It must be opened in Control Panel - Networks and Internet - Network and Resource Center

shared

2. Click Change adapter settings to view the network status.

3. Double click on the adapter that we want to configure.

4. Click on the Properties button and double click on Internet Protocol version 4

(TCP / iPv4) and again the Properties button.

5. Here we choose between Obtain an IP address automatically if our provider has

offered to get the configuration by DHCP (most common); o Use the following IP address to perform manual configuration of IPs, subnet mask, gateway, and DNS.

Creating a home network in windows:

In order to create a home network that allows us to share files and folders, we have to give a name to our team and the working group (this has to be the same in all computers on the network). For this, we right-click on the windows icon that It is on the left in the taskbar and this screen appears:

We click on change settings and a new window appears in which by clicking On changing we write the name of our team and that of the working group. The computer will ask us to restart the computer. Later we go to Control Panel - Networks and Internet -

Network and shared resources center and click on homegroup and then create a homegroup.

We choose which files and devices we want to share and at the end, it gives us a password that

It will be the one that we have to introduce in all the computers in the network in which we will repeat these steps.

Folders can also be shared more easily without having to be in its workgroup. To do this we mark the folder and clicking with the right button click on share with - specific users and then click on add -

we choose everyone's option - share.

DOS Commands for Networks:

There are DOS commands (Enter with cmd) that help us to have information and verify the correct

operation of our network.

ipconfig: It shows us the configuration values ​​of our network. For more information put ipconfig / all and in this way, we would have data such as our IP, gateway, DNS servers or the MAC address of our network card.

ping: It allows us to verify the operation of our network both during its configuration and to detect possible failures in it. The ping command sends a packet of 32 information bits that the destination reads and responds to in the same way so it must match the response information. It also gives us the time it takes for two points to connect remotely. Some practical checking utilities would be:

a) Know the IP of a web page.

ping www.google.es

b) Verify the network card

ping IP of my computer

c) Verify the equipment wiring to the network

ping IP of another computer

d) Verify general wiring

ping gateway

e) Verify internet connection

ping IP web page (216.58.211.99 www.google.es)

f) Verify DNS servers

ping www.google.es

Tracert : con sends echo packets (same as ping) but it shows us the route it takes to the destination we want to reach, showing us on that path data such as the hosts by which passes and the time it takes for each jump to reach the destination. Tracert has an advantage against in ping and is that here we can see how far and host we got in case. we have a failure in communication with the destination. There are also more visual programs that show us all the communication nodes on the map, such as the visual route, but they are paying (you have 15 days free trial). We can also see the physical situation of an IP in web pages like http://www.ip-tracker.org/

Netstat: This command included in all Windows operating systems, allows monitoring and be aware of all the connections established between our PC and the outside world. With the orders are introduced that allow us to see, know, detect and identify connections active established abroad, both incoming and outgoing, its origin and IP address of origin, know the ports that we have open to listen, see and identify the connections incoming and network intrusions on our PC, know if we have programs that establish contact with a remote host, etc.

Thanks