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.