The question we are looking at here is just how long can we expect the 128 bit address set of IPv6 to last before we've run out of IPv6 addresses? And the secondary question is if we assume that we are just a little worried that we are being a little too profligate with these numbers, whether this is something we can quickly rectify without changing the basics of the address plan, or whether there is some more fundamental weakness in the way in which we've been thinking about IPv6.