Why Translate between IPv4 and IPv6?

IPv4 and IPv6 networks are "incompatible". The IETF recommendation has usually been to rely on dual-stack deployment: have both networks coexist until IPv6 takes over IPv4. However, IPv6 growth has been much slower than anticipated. Therefore, new IPv6-only deployments face an interesting challenge, that of communicating with the predominantly IPv4-only rest of the world. A similar problem is encountered when legacy IPv4-only devices need to reach the IPv6 Internet.

The IETF is currently trying to solve these problems. One initial proposal was NAT-PT [RFC2766]. However, it suffered from various issues which eventually caused it to be declared obsolete in [RFC4966]. Recently, there has been a concerted effort coming from the BEHAVE, V6OPS, and SOFTWIRE working groups to engineer a new solution. Discussions at the 71st and 72nd IETF meetings (Philadelphia and Dublin) led to the scheduling of a two-day interim meeting in Montréal in October 2008. IPv4/IPv6 translation continued to be a major focus of interest at the 73rd IETF meeting in Minneapolis, in November 2008.

This translation concerns has resulted in several draft documents. The general framework for IPv4/IPv6 translation is described in [draft-ietf-behave-v6v4-framework]. It also explains the background of the problem, and some expected uses. Another document describes the translation proposal [draft-ietf-behave-v6v4-xlate]. There are two concrete protocol proposals that have much in common: NAT64/DNS64 [draft-ietf-behave-v6v4-xlate-stateful] [draft-ietf-behave-dns64] and IVI [draft-xli-behave-ivi]. A good text comparing the proposals is [draft-wing-nat-pt-replacement-comparison]