Controlling P2P Applications via Address Harvesting: The Skype Story

P2P applications have become a dominant force in the Internet, both as an economic factor and as a traffic contributor. A "battle of power" is ongoing between the application providers and the Internet Service Providers (ISPs) on who will control this traffic. This is motivated by both economic incentives and QoS objectives. Little is known to the ISPs about the architecture of such applications or about the identity of their sessions, these are hidden by the application providers (assisted by their distributed control structure) making the ISPs\´ life harder. We are interested in Skype, as a very popular representative of distributed P2P applications. We explore the possibility of getting control/blocking Skype sessions by harvesting its Super Nodes (SNs), and blocking the network clients from connecting to them. Using experimental results and an analytical model we show that it is possible to collect a large enough number of SNs to block, with a probability higher than 95%. We further use the model to show that our approach is robust against possible strategies that can be adopted by Skype to maximize its resilience to blocking. The results derived and the vulnerability to SN harvesting, though discussed in the context of Skype, are general and may hold true for other Super Node based P2P systems.