Why IPv6: What CCNA Candidates Need to Know About IPv6

One of the components of the current CCNA Exam (640-802) is a basic understanding of the new IPv6 protocol and some transition steps to utilize IPv6 in existing IPv4 network implementations.

But before you begin to study the formats and functionality of IPv6 for your CCNA exam, you should have a firm grasp of why this new protocol is needed and its role in the future of networking.

In this article, we will walk the history of this protocol, investigate some of the issues driving IPv6 to the forefront, and finally look at who is using IPv6 today and what can be expected in the future.


A Brief History of IPv6

As early as 1990, experts began to predict the current IPv4 address space with its current rate of growth would soon run out.

The unicast available IP Classes at the time were A, B, and C. In 1992, Classless Internet Domain Routing, or CIDR, was introduced to summarize IPv4 blocks more efficiently and slow the exponential growth pattern of the global Internet routing table.

Later in 1993, the Internet Engineering Task Force (IETF) recognized the need for a new protocol to address many of the current IPv4 shortcomings and started a working group designated IP Next Generation (IPng) to organize its development.

In 1994, many of the Internet standards committees approved this new protocol and it was assigned version number 6.

As part of early deployments, IPv6 test beds were created to generate exposure to the new protocol starting with the first IPv6 backbone, 6bone, which was created in 1996. The first IPv6 exchange point, 6TAP, was developed one year later at the Chicago STARTAP exchange point.

In 1999, the regional Internet registries (RIRs), the organizations responsible for assigning IP address space, began assigning the first block of global IPv6 prefixes for widespread use. As early as 1996 operating system providers were developing specialized patches to support the new protocol, but most mainline releases were not available with some basic IPv6 capability until 1999.

In 2001, the IPng working group officially changed its name to IPv6.


A Look at the IPv6 Issues

Now that we’re aware of the brief history of this new protocol, let us look more in depth at some of the reasons for why it was needed.

In this article, we will focus on three of the primary issues:

  • IPv4 address exhaustion,
  • growth of the global Internet routing table,
  • and the disparity in regional allocation of addresses.


IPv4 Address Exhaustion

As I mentioned before, the IPv4s address space was seen to be limited and with the development of the World Wide Web, exhaustion of those addresses became more and more apparent.

To illustrate this issue, let us look at the current IP address allocation (Figure 1) computed from data recorded for the Internet Assigned Numbers Authority (IANA) as of January 2010. The IANA is the organization responsible for coordinating the DNS root domain, allocating IP addresses to the RIRs, and managing various Internet protocol number assignments.

Why IPv6 - Figure 1

As you can see from the chart, the unassigned portion of the IPv4 space is now only 10% and other addresses are either private or are not usable as they have been designated for multicast or still slotted for testing or further use (Class D and E addresses).

In 2002, this unassigned portion of addresses was at 28%. Various experts on IP allocation and address exhaustion continue to debate the timeframe when the addressing space will run out. Dates vary from late 2011 to early 2015, but the majority of them believe that 2013 is the most likely target.

The IPv4 address structure is comprised of 32 bits for a total of 232 or 4,294,967,296 addresses. With all the subtractions for network numbers, broadcast addresses, and private or unusable address blocks, the number of usable addresses is much less. IPv6 has a 128 bit structure which supports a total of 2128 or 3.4 x1038 addresses, seemingly enough to provide addresses for the next few decades.

A colleague of mine, who has served on IETF working groups, once told me, “There are enough IPv6 addresses for every blade of grass on the planet.” I believe he might be right.


The Growth of the Global Internet Routing Table

Another issue that has promoted the need for a new IP layer protocol is the rapid growth of the global Internet routing table.

Ever since 1992, the Internet routing table has been on an exponential growth curve. CIDR with its route summarization and the addition of route aggregates have slowed the growth, but the table today does not have a well defined hierarchy and as the size continues to grow, efficient routing will become more difficult.

IPv6 was designed to have a much more hierarchical structure to support aggregate routes for more efficient and scalable routing. To provide a better understanding of the growth issue, Figure 2 shows the growth pattern of the routing table over the past two decades.

Why IPv6  - Figure 2

Figure 2: Global Internet Routing Table Growth from www.cidr-report.org.


The Disparity in Regional Allocation of Addresses

The last issue we will cover today is the regional assignment of the current IPv4 address space. As I mentioned before, the five RIRs are responsible for assigning IP addresses. Each RIR covers a specific region as shown below:

  1. ARIN – North America and parts of the Caribbean and North Atlantic Islands
  2. AfriNIC – Africa and parts of the Indian Ocean
  3. APNIC – Portions of Asia and the Pacific Ocean
  4. LACNIC – Latin American and part of the Caribbean
  5. RIPE NCC – Europe, the Middle East, and central Asia

Due to the fast growth of the Internet in the North American region, nearly 75% of the IPv4 address space has been allocated in that region. Many countries like India, China, and other densely populated areas were left with minimal allocations.

In response to this issue, the IPv6 protocol was designed with a Global Prefix structure that includes plenty of addresses to support balanced allocations across the world.


Who is Using IPv6 Today and What Might We Expect?

Today, IPv6 is deployed in various countries around the world. IPv6 can be deployed as a native IP protocol or “dual-stacked” with IPv4 running on the same interfaces.

China has deployed two of the world’s largest native IPv6 networks and over 50% of South Korean homes utilize broadband connections with IPv6. Japan has developed a nationwide dual-stacked network and European countries are rolling out IPv6 for commercial and government use.

In the United States, the use of this protocol has not been as pronounced. Much of the commercial world has not embraced the need at this time due to the availability of IPv4 addresses in the region. However, the United States Government Office of Management and Budget issued a directive requiring all federal agencies to be IPv6 compliant by June 30, 2008.

IPv6 was not intended to be running on all agencies networks, but all hardware and software must support the new protocol and plans must be in place for a smooth transition to a dual-stacked or native implementation.

This implementation plan and the ever approaching exhaustion of IPv4 addresses will eventually move the North American commercial world to utilize IPv6 mainstream, but only time will tell.



 in Cisco


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