Making multipath TCP friendlier to load balancers and anycast

Duchêne, Fabien [UCL] Bonaventure, Olivier [UCL]

Multipath TCP is a recent TCP extension that enables the utilization of different paths for a single connection. This provides various benefits including bandwidth aggregation and fast handovers on mobiles. A Multipath TCP connection starts with a single TCP connection called subflow and other subflows are added later to increase bandwidth or support failover. One drawback of Multipath TCP is that it is not currently compatible with stateless load balancers which rely on the five-tuple for their forwarding decision. This hinders the deployment of Multipath TCP. We show that this limitation can be circumvented with a small change to the handling of the initial subflow. Clients use this subflow to discover the load-balanced server and the additional Multipath TCP subflows are terminated at a unique address associated to each physical server. With this small change, Multipath TCP becomes compatible with existing stateless load balancers. Furthermore, we show that the same approach enables anycast Multipath TCP services, a major benefit given the difficulty of deploying anycast TCP services. We implement this modification in the Linux kernel and demonstrate its benefits with several micro benchmarks.