<i>From what I can see, he also readily admits that IPv4 and IPv4+ hosts cannot talk to each other, or more clearly, we cannot start using the extended address space before almost everybody has IPv4+ capable software.</i><p>I don&#x27;t know whether to respond to that with &quot;what?&quot; or &quot;yeah, so what?&quot; but I&#x27;m leaning toward the former. IPv4 and IPv4+ hosts would communicate with each other, but IPv4 would only be able to communicate with the overlapping range of IPv4+.<p>Addresses in this range would have initially been relatively valuable but their value would be expected to decrease over time as more hosts started working over IPv4+.<p>I think djb was right, but obviously we&#x27;re unlikely to ever find out.