4. IPv4 and IPv6 integration

4.1 Issues

IPv6 deployment must be seamless. Whether you're an Internet user or connected to a corporate intranet, the IP version changeover must be "at worst" transparent. Well-prepared, this change should in fact open up new service capabilities and move in the direction of simplicity of use.

Integration mechanisms provide answers to the non-trivial problem of service continuity. This problem is non-trivial for the following reasons in particular:

• a 32-bit IPv4 address can easily be included in a 128-bit IPv6 address (known as an IPv4-compatible IPv6 address format), but the opposite is impossible;

• many Internet applications, such as FTP, manipulate addresses directly. In many...