Network

[EN] CCNA Study Notes -1

[EN] CCNA Study Notes – 1

Hi, I will be sharing my learnings from various CCNA documents. Hoping for a productive course for everyone.

Preliminary

What is IP(Internet Protocol)?

In the transportation of the data to reach from somewhere to another, an addressing process is needed. IP Address is a must, let me put it this way. We need a mouth to speak, the mouth here is the IP address. We can’t communicate with our devices without an IP address.

ISPs are the corporations that provide internet to us.

Packet-Tracer-Görsel-1
Packet-Tracer-Image 1

For instance, these devices can’t communicate for not having an IP address

How IP addresses are written is as:

IP Address: 192.168.1.2

You see IPs in your home network like this but the last part switches. Routers are 192.169.1.1 because they are the first device in the network. Apart from the router, devices are given addresses with the last parts increasing from 2.

MAC (Media Access Control)

MACs, carry the address for network adapters. IP addresses are changeable but MAC addresses aren’t, because they are physical hardware addresses, they are written on the network adapter inside the computer.

Sample MAC address: 49:4c:4a:c9:e9:51

A MAC address is made up of 6 octets, first three of them represent the manufacturer. The last three octets represent the device itself.

Ağ Kartı
Network Adapter

You can view your MAC address by typing ipconfig all to CMD

DHCP (Dynamic Host Configuration Protocol)

These values are given with a device with an IP

  1. IP Address
  2. Subnet Mask
  3. Default Gateway
  4. DNS Server Adress

We can enter these ourselves but we have DHCP for doing that. The process of entering these parameters by servers or machines is called Dynamic Routing,  and DHCP takes the charge of it.

DHCP Diagram
DHCP Diagram

 

DHCP requests are firstly initiated by Client. “Gimme an IP address,” he says and the server passes an IP.  For every IP to be unique, DHCP checks up on IP addresses that it will give soon.

In terms of a home network, the network router takes charge of DHCP. Client, the user requests an IP address from the router to give one.

To understand the good of DHCP, let’s think of a network with a thousand computers. Every device will need an IP but it’s a hell of labor work to do so. DHCP arrives in the field and undertakes this.

How to enable dynamic routing though?

The window when you do “Control Panel > Network and Internet > Network and Sharing Center > Change adapter settings > IPv4 Properties” is as:

Dinamik Yapılandırma
Dynamic Confuguration

If the circled options are ticked, DHC Protocol is working. Otherwise, You will assign IP addresses manually if the ones below them are ticked.

DNS (Domain Name Server)

Works in the Client-Server way. Is used to the Hostnames to IP. Hostnames have to become IP because devices can’t communicate with hostnames.

We encounter DNS on websites. What we use on websites “www.pwnlab.me” is a domain. When you type this domain in a web browser, DNS resolves this and turns them into IP addresses.

DNS names have to be unique as IP addresses do.  But for they are unique, there would be chaos.

DNS-Diagram EN
DNS-Diagram EN

A diagram that practically represents the main idea.

The client initiates the request. Request reaches to DNS server, gives the IP address we need.

DNS Diagram
DNS Diagram

The route how domain “www.pwnlab.me” is built:

First, Top Level Domain(TLD) which looks like “.com, .me”. We go to TLD “.me” and ask for a “pwnlab”, TLD says, yes, so that we have a “pwnlab.me” now. We are at Second Level Domain(SLD) now. Lastly, we go to the next stop and ask for a “www”. If there is one, our domain completely is.

In conclusion, we don’t just take the domain from just one place. And this route doesn’t repeat every time, cache steps in, helps to save some internet usage.

To see the DNS of the device we are in, use CMD. DNS Server information is seen when ipconfig /all  is typed:

ipconfig all
ipconfig all

I will show few ways to see if our DNS is working.

Pinging:

Ping atma
Pinging

As you can see, there is a response. Yet another toll is nslookup:

nslookup
nslookup

This command affirms that the domain address has turned into an IP address.

HTTPS

HTTP works as client-server way too. It is in charge of defining the communication rules between the web client and the web server. The client requests something, and the server responds to us.

HTTP_diagram
HTTP_diagram

I didn’t include ISPs in this diagram even though they exist. We could do nothing without ISPs. As the client, we request “pwnlab.me homepage”; it returns the index.html as a response. If there is no such page, it will respond a 404 error.

The difference between HTTP and HTTPS is pretty visual without an abbreviation.

HTTP and HTTPs 

HTTP = Hyper Text Transport Protocol 

HTTPs = Secure Hyper Text Transport Protocol 

Why HTTPs is secure is because every data you send gets encrypted. At HTTP, if someone catches a response in the air, (Burp Suite) they can screen everything so clear.

Telnet & SSH

Both of them are protocols to check up on the device remotely. Telnet works as client-server. There is a  verification process when client requests connecting. Logs in if affirmative.

While Telnet sends data as clear text, ssh encrypts the whole traffic.

FTP

Works as client-server. Adjusts the rules of file sending between FTP client and FTP server.

The client initiates the FTP request, the FTP server confirms, sends the files to local.

We can connect to FTP by going by “ftp” on CMD. “?” Will list the usable commands.

FTP
FTP

NAT

To can see detailed information on NAT, see Salih Öztürk’s post.

You have probably heard that addresses on IPv4 are limited. NAT ensures that the public IP addresses of devices are the same in a home network. That way fewer IP addresses are used.

Packet Tracer

That was the background information for what I will be mentioning soon.

Packet Tracer is an application that is developed by Cisco Networking Academy to help students learn networks. You can prepare for the CCNA exam with this software.

This is the login screen you’ll see after installation(clicking next constantly).  Sign up to the Cisco Networking Academy to log in.

Packet Tracer Giriş
Packet Tracer Login

Logged in interface:

Packet-Tracer-Görsel-1
Packet-Tracer-Image-1

Packet Tracer Network Components

I’ll briefly explain the interface, though you can just find out about them hovering around.

We have some tools we will need. First part is Network Devices. Things like router, switch, hub goes in here.

Network-devices
Network-devices

The second part is End Devices. requests’ last stop are these devices. Computers, tablets, etc.

End-Devices
End-Devices

And Connections, here we have the cable types for connecting devices to each other.

Connections EN
Connections EN

We can drag all of them to the space.

First Networking Test (PC – PC)

We need components to make two device communicate:

  • Source
  • Destination
  • Media

We could put just one device. But it wouldn’t count as communication.

Now we’ll form a communication channel between two computers. First, drag PC from toolbar down there, End Devices. Now we have Source but Destination. Drag another computer to let there be a Destination.

Packet Tracer named the computers PC0, PC1.

İki bilgisayar bağlanmadan
To computers without a connection.

Now we have two devices without a connection. These processes will remain in network adapter because there isn’t a network media. The wireless adapter is required for sending packets wirelessly. Anyway, let’s whether these computers have wireless adapter or not

Network Adapter Check

Double-click a computer to do that:

Bilgisayarın Ağ kartını kontrol etme
PC Network Adapter Check

As you can see from the circled part, this computer uses cabled network adapter. Firstly you’ll need to turn off this computer to change this.

Turn off computer
Turn off computer

Then drag the cabled network adapter to the menu left there, add the wireless network adapter.

Bilgisayardaki kablolu ağ kartını çıkartma
Removing the cabled network card in the computer
Install wifi cable to computer
Install wifi cable to computer
Bilgisayarda kablosuz ağ kartı
PC with wireless NWA

You can mount various modules and network adapters from the left bar there. Let’s put back the cabled network adapter (1CFE) now.

Kablolu Ağ kartını takma
Assembling the Cabled Network Adapter

You’ll need to restart this computer.

Now let’s connect the networking cable. For that, choose the Automatic Choose Connections Type from Connections, then click the two computers. Normally there are various cabling methods for devices in the network, but I won’t refer to them in this first episode.

Kablo Seçme
Choosing Cable
Bağlantı Başarılı
Connection Successful

Successfully connected if there are green arrows.

That’s it for the very first chapter of this series. Later.

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