IPv4+4

The IPv4+4 architecture presented provides an evolutionary approach to the extension of IPv4 address space. It builds on the existence of network address translators (NATs) and private address realms. During and after the transition from IPv4 to IPv4+4 there is no need to change routers, only NATs and end-hosts. End-to-end address transparency is regained incrementally as deployment progresses. The transition process is simple and it provides incentives for networks with both private and public addresses to upgrade and increase transparent reachability. Early implementation experiences are also included.