On 3 February 2011, the Internet Assigned Numbers Authority announced that the final blocks of IPv4 addresses had been distributed. This final allocation signals that IPv4 address exhaustion is imminent, and sooner rather than later we will need to transition to IPv6.

Internet Protocol version 4 (IPv4) uses a 4 byte (32 bit) address format to identify devices on a network. This format can generate approximately 4.29 billion (4.29 x 109) unique addresses. Many of us might be familiar with those addresses in dot-decimal notation, for example “”.

Although 4.3 billion is a significant number, the exhaustion rate for IPv4 addresses has accelerated in recent years. This has been attributed to two key factors:

  • fast growing economies, such as India and China, driving a dramatic increase in Internet users via PCs, portable and mobile devices, and
  • an increase in the numbers and types of devices that are always on and connected to the Internet.

Internet Protocol version 6 (IPv6) was launched in 1999 to eventually replace IPv4. Instead of 32 bits, IPv6 addresses have a 128-bit format, which means that it can offer an almost limitless supply (approximately 3.4 x 1038) of unique addresses. IPv6 also offers a number of advantages over IPv4 by integrating and taking into account some current and anticipated network features and requirements into its design. Examples of the improvements that have been made include:

  • Optional features in IPv4 such as multicast, where one packet being transmitted to many destinations using a single send command, is implemented frequently. As a result, it has become a basic capabilitiy in IPv6.
  • IPv6 offers better Quality of Service support for a broad range of applications.
  • It offers improved authentication and privacy features over IPv4.
  • Unlike IPv4, IPv6 has been designed to support mobile devices through Mobile IPv6. This protocol allows mobile devices to roam between different networks without losing an established IP address.

IPv6 has been designed completely independent of IPv4. The two protocols are incompatible, which means that IPv4 traffic cannot interact with IPv6 modems and routers, and vice versa. Hence IPv4 must eventually be abandoned in favour of IPv6.

Transitioning to IPv6

Migrating from IPv4 to IPv6 can be costly. Devices that support IPv4 only will need to be upgraded and networks reconfigured. Moreover, since the majority of network users still employ IPv4, many organisations are opting to delay their migration to IPv6, noting that there might be little economic benefit to do so unless or until it is absolutely necessary.

As an interim measure, Network Address Translation (NAT) systems are being used to bridge IPv4/IPv6 incompatibility. With these systems, IPv6 users on a network share a single unique IPv4 address through which they communicate to the Internet. However, such NAT systems are fraught with problems, such as bottlenecks due to the system being overloaded with requests for NATs, along with error and security issues due to many users sharing a single IPv4 address.

Nevertheless, in this transition period, websites will increasingly need to support access in both IPv4 and IPv6. Most of the major websites are already running dual-stack protocol, which implements both protocols either independently or in a mixed form.

On World IPv6 Day, which will occur on 8 June 2011, major websites such as Google, Yahoo, Facebook, Akamai, Limelight, and others, will operate solely in IPv6 mode for 24 hours. The purpose of the exercise is to allow for wide scale testing of IPv6 in order to discover any difficulties that might exist, and to prepare for its permanent deployment.

Many of the sites that will participate in this test anticipate that the majority of users (up to 99.5%) will be unaffected. Most clients and users are currently able to communicate in IPv6, since many Operating Systems have already included IPv6 capability in their networking frameworks.  The more critical and larger problem is with getting networks to communicate in IPv6.

What can we do in the interim?

Migrating from IPv4 to IPv6 will take years.  More importantly, a cut-off date by which IPv4 should be abandoned has not yet been established. Although it might be a good idea for the time being not to interfere with systems that are operating flawlessly in IPv4, since the changeover to IPv6 is inevitable, IPv4/IPv6 compatible choices should be implemented in the future. Opportunities when the transition to IPv6 can be made include:

  • when existing hardware or applications need to be replaced or upgraded
  • when current IPv4 address allocations are close to exhaustion
  • when difficulties are being experienced with NAT implementation
  • when there are applications based on IPv6 that you wish to make available on the network.