A premise that was specified for IPv6 design was that the new protocol should coexist with the current protocol (IPv4). In order to make this possible “transition mechanisms” were developed. These transition mechanisms are divided into three groups:
- Dual stack
- Translation
- Tunneling
Dual Stack
This allows simultaneously maintaining both the IPv4 stack as well as the IPv6 stack within the same device. In this way, depending on the stack where the node with which we wish to communicate is implemented, either the IPv4 or the IPv6 stack will be used.
Translation
This transition mechanism performs a “translation” similar to the one performed by NAT, whereby the IPv4 header is transformed into an IPv6 header. Within this group the most well known mechanism is NAT-PT. However, this type of mechanisms are not the most recommendable.
Tunneling
When an IPv6 packet must go through an exclusively IPv4 network “tunnels” may be used. A tunneling protocol “encapsulates” an IPv6 packet within an IPv4 packet so that it can travel through these networks. The packet is “decapsulated” upon arriving at its destination, which must be an IPv6 or dual stack node.
The most common tunneling implementations include 6to4 and Teredo.
