What is an IP Address?

The Internet is a worldwide network of unrelated computers that can only communicate successfully by agreeing to incorporate a set of rules or protocols. One of the most basic tenets of the Internet is the Internet Protocol (IP) address.
An IP address refers to a unique number assigned to each computer on the Internet. The IP number is called an "address" because it serves the same purpose as a home address -- it allows each machine on the Internet to be located by a numerical scheme. A domain name, such as geekofall.blogspot.com, also maps to a numerical IP address. An IP address is analogous to a street address or telephone number in that it is used to uniquely identify an entity.

Dotted Decimals :

Your IP address at home will be different from the IP address at your work office. And that IP address will be different from the one you would have if you used the free wireless hotspot at a coffee shop or hotel.
But they all have one thing in common: They will be in four sections, separated by three periods or dots. That is the common structure for all IPv4 addresses (v4 stands for "version 4").It uses 32 bits to represent an IP address. As more computers are connecting to a network IPv4 is reaching it's limit of providing unique addresses to each computer and hence a new version of the IP protocol (IPv6) has been invented to offer virtually limitless number of unique addresses using 64 bits.

Have you ever wondered what those four sections represent? Here's a quick overview: There will be some technical terms, but they're nothing to be worried about. You will still be able to understand the basics of what's going on with your IP address.

At the heart of everything to do with computers is this fact: Computers have a language and method all their own. Everything you see on your screen has a format that your computer understands and translates into words numbers and pictures.
Computers turn everything into numbers that are a combination of zeroes and ones. If a computer sees the decimal number (a number you recognize) 2,530, it turns that number into a longer string made up of only zeros and ones—0000100111100010. That's called a binary number. Aren't you glad your computer doesn't talk to you in binary code? Computers calculate everything using the binary system. Each of those binary digit is called a bit.

Every little bit counts:

Every IP address is made up of 32 bits. Here's an illustration of what that means:
Let's take the IP address 76.240.249.145. My computer—and all of the networking hardware and software—sees it as a 32-bit address in binary form that is subdivided into four 8-bit parts, called "octets."

76	in binary form is	01001100 (the first 8-bit segment, or octet)
240	" "	11110000 (octet)
249	" "	11111001 (octet)
145	" "	10010001 (octet)

Or you can simply see it in four parts: part1.part2.part3.part4.

What are the four parts about?

• Every IP address—such as 76.240.249.145—is also divided into two sections that define             1) your network and 2) your computer, or host.
• Those two sections comprise the basic structure of IP addresses: the network ID and the host ID. All computers on the same network share the same network ID. Each computer (sometimes called a "network interface") has its own unique host ID.
• The four IP address parts do NOT have to be divided equally—it's not always the case that two parts make up the network ID and two address parts make up the host ID. The network ID may be one, two or three of the parts, leaving the last part for the host ID.

How the parts come together to define the IP address's network ID and host ID also determines what Class of network that IP address is associated with.

• If an IP address's network ID is defined by the first part of the IP address, the computer is connected to a Class A network. Class A networks are very large and could have approximately 17 million hosts/computers connected to it!
• If the network ID is comprised of the first two parts of the address, the computer is connected to a Class B network. Class B networks are smaller than Class A ones and can have about 65,000 hosts.
• If the network ID is comprised of parts 1, 2 and 3 of the IP address, the computer is connected to Class C network. A Class C network can accommodate only about 254 computers...but there can be more than two million Class C networks.

 ISP and IP :

 
Most people are familiar with the idea of an IP address through getting an Internet Service Provider (ISP). The ISP might offer either a dynamic or static address. A static one is a permanent address, while a dynamic address changes with each new Internet session. Every ISP has a unique range of available IP addresses.

Unless one arranges for a static IP address, a dynamic address is automatically assigned in the login process and will persist until the connection is intentionally ended or otherwise disabled. Upon logging in again, a new one is assigned. In each case, machines on the Internet will accept requests and return data to the current IP address of your machine. This IP number becomes part of the "return address" on the "envelope" as the browser requests Web pages, mail, and other online data.

An IP address can be mapped back to a specific user by requesting the log records of the ISP. In the case of unlawful online behavior, for example, law enforcement might punish an ISP for the name, address, and other personal information of the customer that was assigned a specific IP address associated with the criminal activity in question. 
Websites typically track visitors by their IP addresses to see what pages are of interest. Identities can be linked to the address when registration and cookies come into play. A cookie can "tell the site" who the user is, despite a changing IP address. The site may have true or false information, depending on what the visitor has provided.

Though the Internet might feel anonymous, it is not an anonymous environment by default. The IP address is the first and last link to the end-user. In order to surf anonymously, many people choose to "hide" their address by using a website that substitutes its own IP address for the user's. Sites that provide anonymous surfing keep the user's address hidden from the Internet, while acting as an intermediary. Of course, the website providing this service still has a record of the end user's IP address.