Jacopo Cesareo will present his MSE talk on Monday May 7 at 11AM in Room 302 (note room!). The members of his committee are: Jen Rexford, advisor and Michael Freedman, reader. Everyone is invited to attend his talk. His abstract follows below. ------------------------ Traffic filters block clients from communicating with certain Internet destinations. To prevent clients from evading the filtering policies, traffic filters may also block access to well- known anonymizing proxies. In response, researchers have designed more sophisticated circumvention techniques that rely on implicit proxies, lying along the path to unfiltered destinations. An implicit proxy transparently deflects traffic directed to an unfiltered destination toward the filtered destination. However, the effectiveness of implicit proxies highly depends on their presence in paths between clients and unfiltered destinations. In this paper we formulate and solve the problem of proxy placement, and evaluate our algorithms on snapshots of the Internet topology for a variety of client and destination sets. We also consider smart filtering techniques that select alternate routes to avoid implicit proxies, as well as the effects of asymmetric Internet routing. Our results show that a relatively small number of proxies can satisfy a large group of clients across a range of geographic locations.