But as members of the network community, we need to think about this issue and do the right thing. . . . It's important for people that have large address space like ours to be good network neighbors. Huitema asserts that for all practical purposes, the Internet community ran out of addresses in 1992, when the registries started clamping down on requests for space. The move delays running out of Internet addresses by so many days or weeks or months, but it's not a fundamental fix. It's expensive to renumber your network, but Stanford is doing that right now. . . .
Some organizations are willing to make the effort.
This means IPv4 can theoretically accommodate four billion addresses. But because of IPv4 design shortcomings and limits in the routing tables, only a fraction of possible IPv4 addresses can actually be used. Estimates of how many addresses IPv4 can handle range from 150 million to one billion. My belief is that it is very, very hard to push the density above about 160 million addresses. But only an estimated 69 million addresses are actually in use.