Exploiting Multipath Congestion Control for Fun and Profit
Matei Popovici, Costin Raiciu · 2016
Multipath congestion control prefers sending more traffic over paths with lower loss rates. This behaviour is key to achieving resource pooling and efficiently allocating resources in multipath networks. However, loss rates can be manipulated in the Internet by service providers to trick multipath traffic to travel via different paths. We show how providers can use policy drop to artificially increase the loss rate for all traffic using information about client subscriptions (i.e. speed of access links) and per-connection RTTs such that regular TCP throughput is unaffected, and Multipath TCP traffic is rerouted to other paths when alternatives exist. Policy drop is cheap: our prototype does not hold per flow state and can process in excess of 64B 9Mbps on a single machine, or 40Gbps with Internet-sized packets. Finally, we use game theory to understand the implications of policy drop on the Internet ecosystem. Our results show that policy drop will be widely deployed for low-bandwidth subscriptions, and may be deployed for higher-throughput subscriptions too.