Estimation of the Port Number Consumption of Web Browsing

Due to the depletion of the public IPv4 address pool, the internes service providers will not be able to supply their new customers with public IPv4 addresses. Either they give private IPv4 addresses and use carrier grade NAT (CGN) or they move towards IPv6 and provide NAT64 service for the IPv6 only clients to reach the IPv4 only servers. In both cases they must use a stateful NAT/NAT64 solution. When dimensioning a NAT/NAT64 gateway, the port number consumption of the clients is a key factor as the port numbers are only 16 bits long and a unique one has to be provided for every session (when using traditional type NAPT, which one does not include the destination IP address and port number in the tuple for the identification of TCP sessions) whereas a single web client may use several hundred sessions and thus port numbers according to the results in the literature. In this paper, we present a method for the estimation of the port number consumption of web browsing. It is based on the port number consumption measurement of the most popular web sites and combining them using the number of the visitors of the web sites as weight factors. We propose the resulted curve as an approximation of a general profile of the average port number consumption of web browsers after the first click, but not including the web users’ browsing behavior. We also discuss the case of the extended type NAPT, which can reuse the source port numbers towards different destination IP addresses and/or destination port numbers. We propose a formula and give measurement results for the extended type NAPT gateways, too. We disclose the measurement method in detail and provide the measurements scripts under Linux, too. key words: IPv6 transition, NAT64, NAPT, port number consumption, web browsing, lack of ports situation.