All Roads Lead to Rome: An MPTCP-Aware Layer-4 Load Balancer

Multipath TCP (MPTCP) is a promising protocol that aggregates the bandwidth of mobile client's multiple interfaces. However, currently it is still not widely adopted. A key reason for this slow adoption is that the layer-4 load balancers (LBs) used to scale TCP based services in data centers are not MPTCP-aware and forward the multiple TCP subflows of the same MPTCP connection independently to different backends (BEs). In this paper, we present RomanRoads (RR), an MPTCP-aware layer-4 LB which eliminates this hurdle to widespread MPTCP adoption. Compared with prior proposals, RR is easily deployable because it does not change the service provider's network configuration, makes no modification to ordinary TCP protocol and only minimal modification to the MPTCP connection setup process, and supports the case of multiple LBs. We implement RR in the form of a software LB and validate its correctness and high performance through extensive experiments. RR achieves 100% correctness at steady state, no connection disruption during LB churns, and line-rate throughput for packets from 5-tuple seen before. Moreover, we shed light on the desired properties of an LB-friendly multipath layer-4 protocol to provide guidance for future multipath protocol design.