text: 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.
  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" . 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.
   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.
  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)
  - Private Address Space
  - CIDR (Classless Inter-Domain Routing)
  (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
  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
  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’.
  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).
  The size of these RIR are roughly equal to continental size.
  IP addresses are distributed in a hierarchical system. As the operator of Internet Assigned Numbers Authority (IANA) functions, ICANN allocates IP address blocks to these five RIRs. These RIRs further allocate smaller block of IP addresses at national level, ISP and other network operators. In the next step the big ISPs assign the smaller block of IP addresses to the next level of ISPs or to the Internet operators. These steps go on until the end user get the individual IP address for Internet connection.
  Let us examine the critical differences between IPv4 and IPv6.
  1. IP Headers
  2. IP Address Space
  = 32 bits
  = 4,294,967,296 possible addressable nodes
  = 128 bits: 4 times larger in bits
  =~3.4 * 10^38 = 340,282,366,920,938,463,463,374,607,431,768,211,456 possible addressable nodes
  =~53,730,194,312 * billion * billion addresses per person on the planet
  3. IP Address Format
  IPv4’s address format is this.
  IPv6’s address format is given below.
  x:x:x:x:x:x:x:x, where x is a 16-bit hexadecimal field
  Leading zeros in a field are optional.
  Successive fields of 0 are represented as :: but only once in an address.
  4. IP Technology Scope
  5. IP Address Types:
  IPv4 offers the following address types:
  IPv6 offers the following address types:
  Out of IPv4 addresses, The World now depends on IPv6
  In the early 1990s, the IETF realized that a new version of IP would be needed, and the Task Force started by drafting the new protocol's requirements. IP Next Generation (IPng) was created, which then became IPv6 (RFC 1883). IPv6 is the second network layer standard protocol that follows IPv4 for computer communications across the Internet and other computer networks. IPv6 offers several compelling functions and is really the next step in the evolution of the Internet Protocol. These improvements came in the form of increased address size, a streamlined header format, extensible headers, and the ability to preserve the confidentiality and integrity of communications. The IPv6 protocol was then fully standardized at the end of 1998 in RFC 2460, which defines the header structure. IPv6 is now ready to overcome many of the deficiencies in the current IPv4 protocol and to create new ways of communicating that IPv4 cannot support.
  IPv6 provides several improvements over its predecessor. The advantages of IPv6 are detailed in many books on IPv6. However, the following list summarizes the characteristics of IPv6 and the improvements it can deliver:
  - Larger address space: Increased address size from 32 bits to 128 bits
  - Streamlined protocol header: Improves packet-forwarding efficiency
  - Stateless autoconfiguration: The ability for nodes to determine their own address
  - Multicast: Increased use of efficient one-to-many communications
  - Jumbograms: The ability to have very large packet payloads for greater efficiency
  - Network layer security: Encryption and authentication of communications
  - Quality of service (QoS) capabilities: QoS markings of packets and flow labels that help identify priority traffic
  - Anycast: Redundant services using nonunique addresses
  - Mobility: Simpler handling of mobile or roaming nodes
  Internet is a much different place and continuously evolving. Number of new mobile devices are emerging rapidly. Huge data in the form of video, audio, text, and picture is generating a lot of traffic on Internet. And the world is already taking huge strides toward Internet of Everything (IoT). Due to the explosion of newer digital devices which are getting connected on Internet, we currently need a huge number of IP address. Understand that though NAT/PAT did excellent job in slowing down the exhaustion of IPv4 address space, the need for IPv6 is greatly felt today, because IPv6 offers some great features over IPv4.
  IPv6 is becoming a reality. The many years of early protocol research have paid dividends with products that easily interoperate.
  Deployment of IPv6 is not a question of if but when. IPv6 is an eventuality.
  The transition to IPv6 continues to take place around the world. The protocol is gaining popularity with each passing day and is being integrated into more products. There are many IPv6-capable operating systems on the market today. Linux, BSD, Solaris, Microsoft Windows (Vista/7/8/10), and Microsoft Windows Server 2008/2012 operating systems all have their IPv6 stacks enabled by default, and IPv6 operates as the preferred protocol stack. Of course, Cisco equipment fully supports dual-stack configuration, and the number of IPv6 features within IOS devices continues to grow.
  However, the timeline for the deployment of IPv6 is long and difficult to measure. One of the remaining challenges for IPv6 is that few IPv6 service providers exist. Currently, Internet IPv6 traffic is still light compared to IPv4, but it continues to grow.
  IPv6 is the protocol which is capable of providing us more than enough IP addresses and additional features as well.
  - What do think about IPv4 today?
  - Have you migrated to IPv6?
  - What valuable insights do you have about IPv6?
  I request you to please provide me the feedback on this article, your valuable comments will help me to provide you the better information as per your suggestions. In the upcoming articles on IPv6, I will discuss about the various features of IPv6.
  You may like to share the article with your friends, contacts on social-media, e.g., Facebook, Linkedin, Twitter etc, who might be interested in knowing more about IPv6 or sharing their insights with us.
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