The results are surprising: Houston contends that the current trends, if continued, would not exhaust the v4 address space for another 10 to 20 years. It may be that Houston is dead wrong; he admits as much himself – because, at the very least, any `linear' projection is pretty much useless in the face of a disruptive technology or unexpected event. But it's worth knowing that the address equation is much more complex than might be suggested by simple subtraction…