I used the metaphor of dominos in a prior post to illustrate the close inter-relationship among IPv4 address suppliers, namely IANA, each of the Regional Internet Registries (RIRs) and Internet Service Providers (ISPs). Up til now, the "initial domino" fell with IANA depleting its available IPv4 space in early February, 2011. This event was followed only two months later by the APNIC, the RIR serving the Asia Pacific region, to fall next when it reported that it had entered the final phase of its IPv4 allocation policy with only its final /8 of IPv4 space remaining. Today, the European RIR, the RIPE NCC, announced that it too has now begun making allocations from its final /8 of IPv4 address space.
The clock is ticking on IPv4 address space. Unfortunately, it's inevitable. IPv4 space will no longer be available for allocation anywhere at a time in the not too distant future. Even if you have plenty of IPv4 address space, the complexion of the Internet will continue to morph from today's predominantly IPv4-only network to a mixed IPv4-IPv6 network. To reach all Internet users of the future with the ubiquity of today's Internet, you'll need to deploy IPv6 at least for your Internet-facing infrastructure like web and email servers. Of course if your internal users desire to connect to IPv6-only websites that emerge over time, you'll need to consider techniques for enabling this, such as deploying a translation gateway or implementing dual stack on such devices.
There's a lot to think about when deploying IPv6, even on "only" Internet-facing infrastructure. Mike Dooley and I have teamed up to write a forthcoming book on the topic, to be available in early 2013, to help people understand the motivation behind deploying IPv6, the process of assessment, planning, testing and deployment, as well as the technical aspects including consideration of infrastructure, applications, computing devices, security, network management, and of course, IP address planning. More details will follow as we approach publication so stay tuned!