The obvious solution is for networks that need more IP addresses to buy them from organizations that have more than they need. Indeed, this process has already started. Earlier this year, Microsoft paid $7.5 million for two-thirds of a million IP addresses that were previously held by a bankrupt Nortel, suggesting that the going rate for an IP address is around $10.

A market in IP addresses will significantly extend the useful life of the IPv4 address space. Rising prices encourage firms to economize, and this principle applies to IP addresses as much as to any other scarce resource. So far, firms have been using IP addresses wastefully because they’ve been able to get new ones for free. Now that’s no longer true, and firms will have to think harder about whether they’re using their supply of IP addresses efficiently.

So what’s the problem? The American Registry for Internet Numbers, the non-profit organization that has traditionally handed out IP addresses to North American ISPs, has resisted the emergence of a market for IP addresses—at least one it doesn’t control. The organization insists that IP addresses are not property and that address blocks can only be transferred with its approval. ARIN’s policy is to only approve transfers to organizations that ARIN believes “need” the IP addresses. ARIN president John Curran tells Ars that ARIN’s policies were “developed by the Internet community.”