Whether you choose to believe it or not, public IPv4 address space will be exhausted sometime in the next two years -- unless a miracle happens and the internet's early adopters return their Class A networks to the public pool, which would delay the inevitable by a few months or years. And what about the transition from IPv4 to IPv6?
So far, the whole internet ecosystem is successfully ignoring the impeding IPv4 address exhaustion catastrophe. Large carriers are slow to deploy IPv6 services since there's no demand for them. Low-end customer premise equipment (CPE) and mobile device makers are pretending IPv6 does not exist (as the only mobile devices supporting IPv6 on UMTS are the Symbian-based phones).
And most content providers probably don't even know what IPv6 is. Google and other big content providers are an obvious exception, since they don't want to lose a single visitor. Google will do whatever is necessary, including beginning their IPv6 transition as soon as possible.
The grim fact is that it will be impossible to get significant amounts of new public IPv4 address space in a few years. New devices (and users) will have to use IPv6 to connect to the Internet. And the very long tail -- the niche strategy of selling a large number of unique items in relatively small quantities -- of the content curve will not be directly accessible to these users.
The result? Even if service providers like Comcast try to be future-oriented, invest heavily in IPv6 and work with vendors to develop the standards and gear needed to deploy IPv6, they are stuck with the need to access IPv4 servers. Dual-stack deployment -- running IPv4 and IPv6 parallel to one another -- would be an ideal solution, if only we weren't approaching public IPv4 address exhaustion.
Faced with this unenviable situation and the total indifference of large parts of the IT industry, the networking experts turned to Network Address Translation (NAT), the tool that saved them 15 years ago, but even here they couldn't agree on a single workable approach.