What will the transition be like?

Originally, the plan was to use IPv6 to develop a mechanism for its coexistence with IPv4. While these protocols were not designed to interact directly, i.e., IPv6 is not “compatible” with IPv4, both can coexist on the same network. The new version of the protocol was designed with a long transition period in mind, one during which the network would gradually incorporate IPv6 long before the exhaustion of the available IPv4 address space.

This, however, did not happen. In absence of any clear, major commercial incentives, Internet Service Providers (ISPs) and Content Providers (ICPs) did not implement the technological changes needed for a smooth transition.
IANA’ central pool of IPv4 addresses was exhausted in 2011. Regional Internet Registries then entered their exhaustion phases as shown below:

RIR IPv4 Status
APNIC The final /8 is being used since April 2011.
RIPE The final /8 is being used since September 14, 2012.
LACNIC Beginning of phase 3: 15/Feb/2017
ARIN Entered Exhaustion Phase 4 (final /8 since April 24, 2014)Waiting list policies for requests that cannot be met in force since July 1 st , 2015.
AFRINIC Only registry with an IPv4 address pool that will last a few more years.

As for operating systems and end user devices, servers, desktop computers, tablets and smartphones are already incorporating IPv6. Network equipment such as routers have been adding IPv6 support for over a decade.

More information:

– IPv4 Exhaustion at LACNIC

– Economic Aspects of the Transition: CAF-LACNIC Report on IPv6 economicos-de- la-transicion/

– Transition Mechanisms

– Deployment Statistics

– Interactive Economic Modeling of Transition Alternatives (CAF)

– IPv6 for Decision Makers

Transition Mechanisms

IPv6 design considerations included providing mechanisms to allow a smooth transition to the new version of the IP protocol, without the need for an abrupt change. With this idea in mind, several of these mechanisms were created in order to facilitate the coexistence of both versions.

During the early stages of IPv6 deployment it was believed that adoption of the new protocol would be quick enough and that IPv6 would have gained widespread adoption before IPv4 ran out. This, however, did not happen which is why transition mechanisms are an even more relevant topic today.

Transition mechanisms can be classified according to the different techniques they apply:

It is also possible to classify the different mechanisms based on whether they assume that the underlying infrastructure is predominantly IPv4 or IPv6. Although in the beginning there were IPv4 networks that started gradually adding IPv6 access, as IPv4 ran out, providers started considering the deployment of IPv6-only networks. This means that transition mechanisms are needed to allow customers in these IPv6-only networks to access networks that still only support IPv4. Many mechanisms have been proposed and more are currently being discussed in the IETF. The following is a description of the most widely deployed and more mature mechanisms.