eploy NATs in their networks, and give private addresses to their customers. Especially in mobile networks NATs have been widespread between the end user and the Internet. That fact combined with the NATs already existing at end user networks, means that usage of NATs can only increase in the future. In addition to CIDR, NAT is the main reason why IPv4 address space has lasted as long as it has. Although these techniques increase the efficiency of IPv4 address space usage signif- icantly, they do not change the fundamentals of the Internet Protocol and the need for globally routable IPv4 addresses. The IPv4 address space will be exhausted. It has just taken a longer time with these technologies. 192.168.0.3 192.0.2.100 192.168.0.2 192.168.0.1 Figure 1.6 Network Address Translation. Introduction IPv6 History Thus Far Here we'll try to give a very short summary of the history of IPv6, and give a snapshot in time of the current IPv6 deployment. Writing down the current state of the IPv6 deployment is a calculated risk by the authors; by the time this book actually reaches its readers, the IPv6 deployment will have progressed significantly from what is written here. On the other hand, the authors have stated that the major IPv6 deployment will happen next year and we have said this now for a number of years. However, looking at the current IPv6 deployments seriously, it is clear that the technology maturity, and the overall deployment has taken major steps forward during the last few years. There is no reason to expect that this progress will stop. On the contrary, the deployment can only be expected to accelerate as the exhaustion of the IPv4 addresses progresses. 1.8.1 IPv6 Technology Maturity At the beginning of 1990s, the IETF started to investigate new technology options for the technical evolution of the Internet Protocol. The consensus of the IETF decided on the new version of the Internet Protocol - the IPv6. By 1998 the IETF had finished the IPv6 base specification RFC 2460 [4]. At the same time of the stand