CEDRO: an in-switch elephant flows rescheduling scheme for data-centers

Data-center topologies interconnect an ever larger number of servers using a high number of alternative paths to provide high bandwidth and a high degree of resiliency. The state-of-the-art routing strategy is based on Equal-cost multipath (ECMP) which employs static hashing mechanism over packet header fields to spread the traffic over multiple paths. Routing the traffic without considering the size of the flows and the utilization of the paths might cause congestion due to the collision of multiple large flows on a same downstream path. We present CEDRO, an in-switch mechanism to detect and reschedule colliding large flows. By exploiting the latest advances in SDN programmable network devices, we offload to the network the detection of both the elephant flows and the path congestion conditions and the rescheduling mechanism. CEDRO is able to promptly cope with path congestion and failures directly from the dataplane, regardless of the availability of the external controller. We implemented CEDRO in an emulated SDN network and tested it against realistic traffic scenarios. Numerical evaluation shows CEDRO is able to improve the average and 95-th percentile of the Flow Completion Time compared to ECMP.