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IPv4 Address:

IP or Intenet Protocol is the basic fundamental thing of networking. We all know what is IP address.

But I am repeating once again.

It is a unique address of a machine connected to any network or internet, so that it can be identified easily. You can say it is a unique identifier just like your phone number.

Due to this IP address one computer or any device such as mobile, tablet or a router can communicate with each other and sends data packets. Even a web server and website also have their own IP address.

IPv4 is rapidly used everywhere for past years.It is a 32-bit address.which looks like-> a.b.c.d where a, b, c, d are four numbers between 0-255.Example:172.16.5.2.But why it is 255 not more than that?

See, the total address is 32 bit. Which has four parts. So, each part is 8bit. so, a, b, c, d all are 8-bit number.
As you all know computer do not understand anything other than 0 and 1. same as here. The 8-bit numbers are technically binary numbers. But we generally expressed it as a combination of four decimal number to remember easily.
So, what is the minimum number that we can express through a 8 bit binary??? 00000000 that means decimal 0. and what is the maximum number you can express ????11111111 that means 255.Total 256 number can be written in every part of IP address. So, total numbers of IPv4 address are 256x256x256x256=4294967296. But as the number of IPv4 were getting lesser than device if everyone get a static IP address, Scientists invented a new type of IP address which is known as IPv6.

ISP or Internet service Providers buy their own IP range to give their customer an IP when they connect to internet. Class A IP is most costly as maximum number of IP address is obtained from a single range of IP.You will understand it when you will learn subnetting.
There are two types of IP address according to use.

What is Private IP?

It is an IP provided by your router to communicate within LAN not the internet.Any private IP can not go to the internet.If any packet try to go, the packet will be automatically dropped by the router.
You can check your private IP by going command prompt and type 'ipconfig' and enter in Windows system. and if you are a Linux user go to terminal and type 'ifconfig'.
Three ranges of private IP are there.10.0.0.0-10.255.255.255 , 172.16.0.0-172.31.255.255, 192.168.0.0-192.168.255.255.

It is your IP address to communicate through the internet.
You can check it by going some websites like www.ipcow.com, www.ipbatade.com etc.
Basically, your public IP is the IP of that particular interface of your router that connects to the internet.
So if you and your friend are connecting to the Internet through the same router.Both you will get same public IP address but your private IP will be different.

So you may ask that I am sending a request for www.google.com and my friend is sending request for www.facebook.com via same router.But we have never seen that the request got interchanged even we have same Public IP.

Basically, what happens, when you send a request through router it notes down your private IP and also remembers that you requested for www.google.com But the web server of website don't know that particularly you have sent that request.Web server sees that the request is coming from the interface of the router that connects to the internet.Web server just replies to router.Then router gives the response to you.

Take an example: You are in a Big hotel.You have intercom landline phone in your room.You are in room number 400 and your friend is room number 500.So if you pick up your phone and dial 500 you will connect to your friend.So it is like your LAN and the number 400 and 500 is like your private IP.But you can not use your 400 phone number to connect to your mom outside the hotel.For that, you have to call to reception and tell them to connect to your mom's mobile number.right?But your mom will see the phone number of the reception not your intercom number.So that reception number is your Public IP address.and reception works as router which has two interface one which connects to the internet or outer world and the other which is connect to intercom or LAN.