Migration from IPv4 to IPv6

Migration from IPv4 to IPv6: It is Easier to Nail Jell-O to the Wall than Understand the Mandates and Timing

It has often been said that anything can be proved with statistics, and that may well be the case. This post describes an exercise in statistical analysis, in order to make some predictions about when certain events may take place; in this case, the date and time for the required transition from IPv4 to IPv6.

The growing popularity of mobile and fixed-network devices that require Internet connectivity is rapidly depleting the pool of available public IPv4 addresses. This rapidly approaching depletion of IPv4 address has been known for many years, but, the prognostication of the exact date and time for this situation has been argued many times, in many different and diverse venues. There has never been a credible agreement between the “experts,” either individually or as a member of a recognized group. What is universally agreed upon, however, is that this situation is now beginning to seriously impede emerging Internet markets around the world.

For instance, until the last five years, China has had fewer public IPv4 addresses allocated than Stanford University. And, the U.S. Department of Defense (DOD) had more IPv4 addresses than all of Asia. This wasn’t due to any geopolitical boycott of China or Asia. It’s just that this situation existed because when IP addresses were doled out 40 years ago, the Internet was a DOD project and Stanford was heavily involved. As a result, Stanford was awarded and kept a large block of addresses for themselves.

Asia, China in particular, following massive economic growth, is a relatively new and growing market for IPv6 because there is so little legacy infrastructure in place. With the accelerating growth in Chinese business and personal requirements for Internet connectivity, designers are going directly to IPv6 networks and only using bridge connections to IPv4. It is accepted within the industry that China and Taiwan are on track to design and directly install an impressive IPv6 infrastructure, whereas the private sector here in the U.S. is lagging well behind. This same growth, along with the associated need for large allocations of public IPv6 addresses, is also being seen in India.

The one exception to any fixed, drop-dead change over requirement is the Federal government, which has mandated that all government agency network backbones have to speak IPv6 in the very near future. However, in reality, there is considerable slippage in the migration dates.

The obvious solution to solve this approaching Internet shutout of new users is to move to IPv6, which has 128-bit addresses. That comes out to 340,282,366,920,938,463,463,374,607,431,768,211,456 possible public addresses. To put this incredible number into an easier-to-understand concept, these IPv6 addresses provide five IPv6 addresses for ever square meter on the face of the earth, including the water.

In most regards, IPv6 is a conservative extension of IPv4. Most transport and application-layer protocols need little or no change to operate over IPv6. Also, IPv6 specifies a new packet format, designed to minimize packet-header processing. Since the headers of IPv4 packets and IPv6 packets are significantly different, the two protocols are not interoperable.

While the two biggest reasons why network designers will want to migrate to IPv6 remain as the need for more public addresses and mandates from different government organizations, IPv6 includes some very attractive features and migration tools.

Address Assignment Features:
IPv6 address assignment allows easier renumbering, dynamic allocation, and recovery of addresses, with great features for mobile devices to move around and keep their IP addresses, avoiding having to close and reopen an application.

IPv6 hosts can configure themselves automatically when connected to a routed IPv6 network using ICMPv6 router discovery messages. When first connected to a network, a host sends a link-local multicast router solicitation request for its configuration parameters. If configured for this process, routers respond to such a request with a router advertisement packet that contains network-layer configuration parameters.

In addition, a network may use stateful configuration with the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) or hosts may be configured statically.

Ipv6’s huge address space makes for much easier aggregation of blocks of addresses in the Internet. The larger 128-bit IPv6 address, versus the 32-bit IPv4 address, allows more flexibility in designing newer addressing architectures, as well as providing large enough address spaces for predicted future growth of the Internet and Internet related technologies. A new addressing format, called the Aggregatable Global Unicast Address Format, has been developed to help solve route complexity scaling problems with the current IPv4 Internet.

No Need for NAT/PAT:
Using publicly registered unique addresses on all devices removes the need for NAT/PAT, which also avoids some of the application layer and VPN tunneling issues caused by NAT.

Internet Protocol Security (IPsec), the protocol for IP encryption and authentication, forms an integral part of the base protocol suite in IPv6. IPsec support is mandatory in IPv6. This is unlike IPv4 where it is optional but usually implemented. IPsec, however, is not widely used at present except for securing traffic between IPv6 Border Gateway Protocol (BGP) routers.

Header Improvements:
A number of significant simplifications have been made to the packet header. In addition, the process of packet forwarding has been simplified in order to make packet processing by routers simpler and more efficient.

The packet header in IPv6 is simpler than that used in IPv4, with many rarely used fields moved to separate options. In addition, IPv6 routers do not perform fragmentation.

Significantly, the IPv6 header is not protected by a checksum. The integrity protection is assumed to be assured by both a link layer checksum and a higher layer (TCP, UDP, etc.) checksum. In effect, IPv6 routers do not need to re-compute a checksum when header fields (such as the TTL or Hop Count) change.

The Time-to-Live field of IPv4 has been renamed to Hop Limit, reflecting the fact that routers are no longer expected to compute the time a packet has spent in a queue.

Transition Tools:
Even though IPv6 solves a large number of significant problems, an overnight migration from IPv4 to IPv6 is not possible. For one thing, the actual, physical number of devices installed in existing world-wide network infrastructures is well into the billions. And, in some cases, even if you wanted to migrate to IPv6, the actual hardware devices, or their installed software, might not provide IPv6 support. Also, when planning for such a transition, the issue of budget and cost could become a show stopper.

In my next post we will examine the main options and the basic implementation of processes used for providing a carefully planned migration and transition from IPv4 to IPv6.

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