As the free pool of IPv4 addresses reaches its end, we looked at the evolution of the amount of unassigned IPv4 address space over time. By ‘unassigned’, we mean address space not yet allocated to a Local Internet Registry (LIR) or assigned to an end user. LIRs are typically Internet Service Providers or enterprises operating an IP network.

See our findings in the graph below.

The graph shows that the decline of IPv4 has been mostly linear. This means that the Regional Internet Registries (RIRs) have been allocating roughly ten /8s1 each year since 2004. There was a small decrease in allocations in 2008—due undoubtedly to the economic crisis—before accelerating again in mid-2009.

Thirty-three unassigned /8’s of IPv4 addresses remain as of 1 October 2010. An overly simplistic extrapolation would mean that the RIRs still have three years left to hand out IPv4 address space. This is no reason to relax. We have clearly entered the last phase of available IPv4 address space. In 2010 the need for IPv4 addresses exceeded the long term average. RIRs handed out thirteen /8s in the last twelve months. If this trend continues or accelerates, the lifespan of the unassigned IPv4 address space will be significantly shorter.

Also, due to the difference in the regional communities, it is likely that one region will run out of IPv4 space while another may still have more than one /8 left.

Three years is really the upper limit. An exact run-out date is difficult to forecast because it doesn’t only depend on mathematical modeling but also on address policies.

One might wonder: ‘Why has the number of allocations been so stable over time when the number of LIRs has been increasing at the same time?’. There is no clear answer to this question. The reason is likely to be a combination of the increased deployment of Network Address Translations (NATs) and the increased relevance of IPv4 conservation within the RIR communities over time.

For more information about the method used, please refer to “Interesting Graph—IPv4 Unassigned


1 One /8 of IPv4 address space contains 128 networks (27). Each of these networks contains 16.777.216 addresses (224).

Written by Mirjam Kuehne