The Impact of Port-Based Address-Sharing on Residential Broadband Access Networks

The looming depletion of the public IPv4 address space has recently inspired a number of proposals intended to work around the inevitable address shortage. Broadly, all of these can be classified as address sharing, tunneling and translation mechanisms. While IPv6 is the proper solution to the problem as it simply makes more addresses available, the deployment hurdles of IPv6 make it questionable whether it will be universally available once the IPv4 address pool runs out. In this paper we focus on one of these solutions, namely A+P, that allocates a "fraction" of an IP address to end hosts by restricting the usable port range. We compare a number of strategies to use and reuse port numbers. Based on data from an ISP\´s access line serving nearly 7000 residential broadband customers these strategies are analyzed. To this end, we performed a hypothetical optimization exercise to find the optimal number of customers that can share a single IPv4 address.