IPv4 was never intended to last forever, and by the mid-2000s, many experts optimistically believed IPv4 would be essentially retired by the 2010s, replaced by a vastly superior IPv6 protocol.

As the number of available IPv4 addresses dwindles, Cox suggests that we could reuse the 'Class E' IPv4 address space defined in RFC1112. The Class E space runs from 240.0.0.0 to 255.255.255.255 ...