Whenever we publish stories about the IPv4 address depletion or IPv6, people make comments along the lines of "does MIT really need a class A IPv4 block with 16,777,216 addresses?" Apparently Interop, the holder of the 45.x.x.x block since 1995, no longer needs that much space. They're now returning 99 percent of it to ARIN, the American Registry for Internet Numbers, which handles IP address distribution in North America. Interop is holding on to a small fraction of the 45/8 block that's currently in active use.

As explained earlier this week, we're now going through about one of these blocks of 16.78 million addresses per month, so this infusion extends the lifetime of the IPv4 address space by one month. It's currently unclear whether ARIN will hold on to the returned addresses, or if those will flow back into the global pool—there is currently no policy that allows for the latter, but there is an active community-based policy creation mechanism so this lack of policy may be remedied in the forseeable future.

In a statement, Interop said it "is pleased to serve as an example for other network operators." ARIN CEO and president John Curran took the opportunity to once more stress that network operators should start preparations now for making their public-facing servers IPv6-reachable. Behind the scenes, ARIN has been working hard to get holders of large legacy address blocks to return what they don't need, but progress has been limited so far. However, even if half of the current 91 legacy class A or class A sized blocks are eventually returned, this will only hold off the depletion of the IPv4 address space for about three additional years.