In Exponential IPv6 Part II, I looked at the recent rise in IPv6 uptake, which appears to be in the early stages of the S-shaped technology adoption curve. This starts out slowly, rises exponentially, slows again as the technology approaches saturation, and tapers off.

In a talk at the recent Australian IPv6 Summit 2012, Fred Baker showed a version of this curve (right) with some surprising observations (2.5MB pdf). He stated when an emerging technology reaches about 28% penetration its success is almost unstoppable. At around 70%, the technology it’s replacing is being turned off.

But most interesting is the period of co-existence in between: Fred Baker thinks in the case of IPv6 there will not be the drawn-out dual-stack environment others have predicted will hang around for a decade or more. He believes it will last just a single equipment life cycle – a few years at most.

This is because a dual-stack environment is very expensive in terms of equipment, training and system administration – every relevant service and task must be coordinated over two different network protocols, an operational and security nightmare. A single-protocol network is clearly a cheaper proposition. Once the move to IPv6 begins, it makes financial sense to go fully IPv6, and just handle instances of IPv4 at the boundaries, as islands of increasingly irrelevant software.

More puzzling is the arrow at the bottom of Fred’s graph: ‘We are here: 15% worldwide’. Fifteen percent? But isn’t the level of IPv6 adoption for end-users around 1%? Yes, but there are a number of ways of measuring IPv6 adoption, and the user level may be the least useful of all. The Cisco IPv6 Lab offers a better insight into IPv6 adoption, globally and per-country, drawn from four areas of implementation:

– IPv6 prefixes: the allocations, routeability and activity of IPv6 address prefixes.

– Transit autonomous systems: the IPv6 capability of networks on the intermediate paths between other systems.

– Content availability: the websites visible via IPv6 DNS and responding to requests from IPv6 systems.

– Users: the relative numbers of people using IPv6 to access websites.

A weighted metric of these four measures indicates much of the world’s IPv6 penetration now lies between 12 and 32 percent. For example, China is 13%, Brazil 16%, India 25%, Japan 27%, USA 31%. (Australia is 22%.) The great IPv6 pioneers, France and Romania, are at 50% and 65% respectively on the Cisco combined metric.

Suddenly a takeoff point of 28% of IPv6 worldwide doesn’t look very far away at all, and in the influential United States, that threshold has already been passed. Just one equipment cycle from now, IPv4 could well be as fragmented and isolated as IPv6 was itself a few years ago.