The transition does not require any global coordination. Your sites and Internet service provider (ISP) can transition at their own pace. Furthermore, an effort has been made to minimize the number of dependencies during the transition. For instance, the transition does not require that routers be upgraded to IPv6 prior to upgrading hosts.
Different sites have different constraints when transitioning. Also, early adopters of IPv6 are likely to have different concerns than production users of IPv6. RFC 1933 defines the transition tools currently available. The rationale for transition is either the lack of IPv4 address space or the required use of new features in IPv6, or both. The IPv6 specification requires 100 per cent compatibility for the existing protocols and existing applications during the transition.
To understand the transition approaches, the following terms have been defined.
IPv4-only node – A host or router that implements only IPv4. An IPv4-only node does not understand IPv6. The installed base of IPv4 hosts and routers that exist before the transition begins are IPv4-only nodes.
IPv6/IPv4 node – A host or router that implements both IPv4 and IPv6, which is also known as dual-stack.
IPv6-only node – A host or router that implements IPv6, and does not implement IPv4.
IPv6 node – Any host or router that implements IPv6. IPv6/IPv4 and IPv6-only nodes are both IPv6 nodes.
IPv4 node – Any host or router that implements IPv4. IPv6/IPv4 and IPv4-only nodes are both IPv4 nodes.
Site – Piece of the private topology of the Internet that does not carry transit traffic for anybody and everybody. The site can span a large geographic area. For instance, the private network on a multinational corporation is one site.