When two or more devices wants to communicate with each other they need unique ID on that network. Internet Protocol (IP) addresses are the unique numbers assigned to every computer or device that is connected to the Internet. Among other important functions, they identify every device connected to the Internet, whether it is a web server, smartphone, mail server, or laptop, etc.

After years of rapid Internet expansion, the pool of available unallocated addresses for the original Internet Protocol, known as IPv4, has been fully allocated to Internet Services Providers (ISPs) and users. That’s why we need IPv6, the next generation of the Internet protocol that has a massively bigger address space than IPv4.

IPv4 Connectivity with Internet


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A Brief History of IPv4 and IPv6

Internet Protocol was introduced first time in January 1980, as a standard in the RFC 760.

Motivation behind the RFC 760 was stated as given blow:

The Internet Protocol is designed for use in interconnected systems of packet-switched computer communication networks. Such a system has been called a "catenet" [1]. The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations, where sources and destinations are hosts identified by fixed length addresses. The internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through "small packet" networks.

IPv4 RFC 760
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[1] Cerf, V., "The Catenet Model for Internetworking," Information Processing Techniques Office, Defense Advanced Research Projects Agency, IEN 48, July 1978.

At the time of standardization of IPv4, the world population was around 4.41 billion in 1980. The ratio of IPv4 address to the world population was 1:1. In 1980, there was no www (world-wide web), no mobile devices, as the major devices were mostly mainframe and minicomputers.

IPv4 And Population Ratio In 1980

In fact, World Wide Web was introduced in 1990s, and soon everyone was getting on internet. Subsequently the IPv4 routing tables were growing so rapidly that it reached to 20,000 routes in 1994. IETF realized that it would soon run out of IPv4 address space.

In order to slow down the running out of IPv4 addresses, IETF introduced solutions—Short-term solutions as well as Long-term solutions

Short term solutions included:

NAT (Network Address Translation) & PAT (Port Address Translation)
Network Address Translation

Private Address Space
IPv4 Private IP Address Range

CIDR (Classless Inter-Domain Routing)
Classless Interdomain Routing CIDR

(Recently I published an article on the topic of : How to configure NAT & PAT on Cisco Router? You may like to visit to this fasinating article too.)

Long term solution was emphasized as IPv6, (e.g., 2001:ABDA:0000:0000:0000:0001:3635:4852)

Evolution in Internet Protocol

Graphical History of IPv4

IPv4 Evolution History

IPv5:

It was an experimental protocol and is no longer used, although some of the concepts it developed have been incorporated into other protocols.

Graphical History of IPv6

IPv6 Evolution History

Basic Questions about IP Addresses

Let us walk through with some basic questions that arise in our mind when we discuss about the IP addresses.

Q. What is an IP address?

IP address is a shorter way of saying ‘Internet Protocol address’. IP addresses are the numbers assigned to computer or device network interfaces. Most of the time, we use ‘name’ to access other device or resources on a network. In case of Internet we use URL e.g. www.example.com in the web browser, and behind the scene computer, however, translates that URL into the IP address of that destination.

Q. Why do we need IP addresses?

IP addresses play a major and essential role in the data transfer between the networking devices. In the absence of IP addresses, the networking devices like computers, servers, telephones, cameras, printers, etc. will not able to communicate with each other.

Without IP address, if we want to transfer the data between the devices, then we would have to do manually, with the help of CDs, DVDs, hard disks or flash storage, such as a USB drive. That will be just too cumbersome and possibly erroneous. Since IP addressing facilitates the network connectivity among all sorts of devices, we are able to send data to all directions or destinations so easily. We are daily performing a large number of tasks on our network and Internet conveniently just with a mouse ‘click’.

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Q. What is the difference between a Private IP address and a Public (unique) IP address?

Before understanding the difference between the Private IP and Public IP, we need to have a very clear understanding about the Private network and the Public network.

Private network means, the network which belongs only to us personally (home, company, organization, campus, etc.) and the Public network means, the network which belongs to everyone or others as well like Internet.

At the protocol level, there is no difference between the public and private IP addresses. But organizationally, private addresses are distinct, because they can be used within single administration and not on the wider internet.

This is because private addresses are set aside for use by anyone without any global coordination. You can identify that an address is from a block of private addresses, if it:

Begins with 10. (i.e., 10.0.0.0 through 10.255.255.255)
Begins with 172.16. through 172.31.
Begins with 192.168.
With the help of these private IP addresses, you cannot access the public network i.e. Internet. And when you find that your computer is assigned a private address, but you still are able to access services over the Internet, then it means that your computer is probably behind a Network Address Translator (NAT), which lets lots of computers share a single unique IP address.

I want to explain little bit about the distribution of the IP addresses in the next section.

Q. How are IP addresses distributed?

The distribution of the public IP addresses is managed by the registries or ISP and these address are allowed to be routed on the Internet.

For the distribution of IP addresses, the whole world is divided into the five Regional Internet Registries (RIRs).

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