4+4: an architecture for evolving the Internet address space back toward transparency

We propose 4+4, a simple address extension architecture for Internet that provides an evolutionary approach to extending the existing IPv4 address space in comparison to more complex and disruptive approaches best exemplified by IPv6 deployment. The 4+4 architecture leverages the existence of Network Address Translators (NATs) and private address realms, and importantly, enables the return to end-to-end address transparency as the incremental deployment of 4+4 progresses. During the transition to 4+4, only NATs and end-hosts need to be updated and not the network routers. The 4+4 architecture retains the existing semantics of Internet names and addresses, and only proposes simple changes to the network layer that focus entirely on address extension. Encapsulation is used as the main tool to maintain backward compatibility. We present the design, implementation, and evaluation of the 4+4 architecture and discuss our implementation experiences and results from local and wide-area Internet experimentation. The 4+4 source code is freely available from the Web (comet.columbia.edu/ipv44) for experimentation.