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Recovering IPv4 Address Space

6 February 2008
By Leo Vegoda

More IPv4 /8s returned to an “IANA – Reserved” status in 2007 then ever before.

With help from the Regional Internet Registries, three /8s were returned in 2007 and last month we recovered one more. We now have 43 unallocated /8s. Here’s a table showing the details of the returned blocks.

/8 Year Help from
46 – BBN 2007 BBN and ARIN
49 – US DoD 2007 ARIN
50 – US DoD 2007 ARIN
14 – Public Data Net 2008 Network Operators

Despite this windfall we are unlikely to see any more whole /8s returned to the IANA free pool. Our investigations indicate that the other legacy “Class A” assignments are all at least partially used. Recovering the space in those blocks would require large companies to engage in expensive renumbering exercises.

But more importantly, it would not buy us very much time. We allocated more than one /8 per month in 2007, so to gain even one year would require a huge amount of renumbering by the users of more than a dozen legacy assignments.

Geoff Huston’s mathematical projection suggests the IANA free pool will be empty before the second half of 2011 and the RIRs’ pools will run out barely a year later. Of course, whatever mathematical models he uses, he cannot account for the very human possibility of a run on the bank.

Address recovery cannot extend the life of the IANA free pool by more than a few months.

It is possible that unused portions of the legacy “Class A” and “Class B” will be returned to the RIRs free pools. Alternatively, it is possible people with partially used legacy assignments will wait for a variant on the policy proposals in the RIPE and APNIC communities to emerge and then engage in remunerated renumbering and address transfer programs.

Whatever actually happens in the next few years, we can be sure that anyone needing large amounts of address space for a rapidly growing network will have to deploy IPv6. IPv6 deployment in the Internet’s core infrastructure is continuing and network operators at ISPs and enterprises need to plan for a world where their users will need to communicate with systems on both IPv4 and IPv6.


Leo Vegoda