The point to be made here is that the origins of the Internet so many years ago held a belief that interconnectivity ought to be pervasive. NAT architectures in the network core speak directly against this. It is true for many operators that some form of NAT is part of an overall transition strategy. The current user community does not understand IPv4 or IPv6 nor why this additional IP network matters to them.
The common belief I consistently hear is that when dual-stack is not possible, dual-stack lite is the lesser of all NAT evils. This has a true benefit to the user. Native dual-stack simply means the end user has IPv6 service alongside IPv4 for some time until IPv4 is quietly turned off.
Dual-stack lite has the benefit of tunneling subscriber IPv4 data within IPv6 from the CPE into the network and applying only one NAT at the provider side. This helps with the ‘broken-ness” dual NAT designs would impose on customers. Examples of “broken-ness” are easy to find from Skype to online gaming to VPN services all no longer working as a result of dual NAT actions in the network. These will be the future support phone calls for the operator not yet prepared for IPv6 service rollout.
It should be clear for everyone that the business justification for IPv6 is to stay in business. So I hope you will join us and the rest of the Internet community to mark IPv6 world launch day, because NAT is evil, and after June 6th, there is no turning back.