IPv6: The Next-Generation Internet Layer Protocol

Many of the current Cisco certifications require a working knowledge of IPv6. As you begin your studies of this next-generation Internet Layer protocol for packet-switched internetworks, I thought it might be interesting to share some of the background on this successor to IPv4 with you.

Internet Protocol version 4 (IPv4) has been at the core of a standards-based internetworking process on the Internet for many decades, and is the protocol with which everyone is most familiar. IPv4 was originally described in IETF publication RFC 791 in September 1981. At about the same time, the Department of Defense standardized it as MILSTD-1777.

Because IPv4 was designed to use a 32-bit word to define an IP address, it was limited to providing 4,294,967,290 unique layer-three logical addresses. At the time of its acceptance as a standard, it was thought that this was sufficient address space for any future network needs.

However, the originators of this protocol had no possible way of knowing what the Internet and the World Wide Web would evolve into in future years. In addition to reserving many possible addresses for special purposes such as private addresses (approximately 18 million addresses) or multicast addresses (approximately 16 million addresses) it was obvious they never envisioned the number of addresses that would be required to support You Tube, Twitter, and e-Bay.

Since the 1980s, it has become apparent to everyone that the number of unique IPv4 addresses that were available to support new mobile devices, and always-on devices such as DSL and cable modems, along with the rapidly expanding number of personal and business Internet users, were being exhausted at an alarming rate. A rate never initially anticipated in the original design of the network.

In early 1992, several proposed solutions were circulated to overcome this serious situation that, if not addressed, would bring an end to Internet growth and the introduction of new systems and applications. By the end of 1992, the Internet Engineering Task Force (IETF) announced a call for white papers and the creation of the “IP Next Generation” (IPng) working groups. And, by 1996, a series of RFCs were released that defined Internet Protocol Version 6 (IPv6), starting with RFC 2460.

One of the most important features of IPv6, which directly solves the problem of Layer-Three address exhaustion in IPv4, is the availability of a much larger address space. Instead of a 32-bit word, IPv6 addresses are identified with a 128-bit word. And, to put this new address space into perspective, IPv6 will provide approximately 2 to the 95th power addresses for each of the roughly 6.5 billion people alive today. It is estimated that IPv6 will provide all of the needed unique addresses for many, many years to come.

It must be recognized that the need to ensure geographical saturation with a ready supply of addresses was an important driver for the creation of this new protocol. However, it was not the sole consideration. The longer address space allows a better and more systematic and hierarchical allocation of addresses and efficient route aggregation. Network management and routing has been designed to be much more efficient than with IPv4.

As you pursue your studies for the CCNA exam, you will need to become familiar with IPv6: global unicast addressing, routing, and subnetting, protocols and addressing, configuring routing and routing protocols, and transition options.

Author: David Stahl

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