Estimating IPv4 address space usage with capture-recapture

As of April 2013 almost 95% of the IPv4 address space has been allocated. Yet, the transition to IPv6 is still relatively slow. One reason could be existing “IPv4 reserves” - allocated but unused IPv4 addresses. Knowing how many addresses are actively used is important to predict a potential IPv4 address market, predict the IPv6 deployment time frame, and measure progressive exhaustion after the IPv4 space is fully allocated. Unfortunately, only a fraction of hosts respond to active probes, such as “ping”. We propose a capture-recapture method to estimate the actively used IPv4 addresses from multiple incomplete data sources, including “ping” censuses, network traces and server logs. We estimate that at least 950-1090 million IPv4 addresses are used, which is 36-41% of the publicly routed space. We analyse how the utilisation depends on various factors, such as region, country and allocation prefix length.