In this paper we introduce a mechanism for hosts to use applications of any IP version capability (IPv4-only, IPv6 only, or dual IPv4/IPv6) regardless of the IP version of their network communication (IPv4 or IPv6), without any modification to those programs. DAC effectively shields the application layer IPv4/IPv6 operation from the underlying IPv4/IPv6 communication between the hosts. The authors consider the provision of this kind of functionality an essential condition for the changeover towards IPv6 to succeed. The proposed mechanism is a generalisation of an experimental protocol called Bump-in-the-API (BIA)