Collaborative and privacy-preserving estimation of IP address space utilisation

Exhaustion of the IPv4 address space is driving mitigation technologies, such as carrier-grade NAT or IPv6. Understanding this driver requires knowing how much allocated IPv4 space is actively used over time - a non-trivial goal due to privacy concerns and practical measurement challenges. To address this gap we present a collaborative and privacy-preserving capture-recapture (CR) technique for estimating IP address space utilisation. Public and private datasets of IP addresses observed by multiple independent collaborators can be combined for CR analysis, without any individual collaborator's privately observed addresses leaking to the others. We show that CR estimation is much more accurate than assuming all used addresses are observed, and that our scheme scales well to datasets of over a billion addresses across several collaborators. We estimate that 1.2 billion IPv4 addresses and 6.5 million /24 subnets were actively used at the end of 2014, and also analyse address usage depending on RIR and country.