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Equal-cost multipath (ECMP)-based traffic engineering (TE) methods are commonly used in intra-data center (DC) networks to improve the transmission performance for east-west traffic (ie, traffic from server to server within a DC).However, applying ECMP on inter-DC wide area network (WAN) offers limited performance enhancement as a result of irregular network topology. Since TE can be intelligently and efficiently realized with software-defined networking (SDN), SDN-based multipath becomes a popular option. However, SDN suffers from scalability issue caused by limited ternary content-addressable memory (TCAM) size. In this paper, we propose an SDN-based TE method called dynamic flow-entry-saving multipath (DFSM) for inter-DC traffic forwarding.DFSM adopts source-destination-based multipath forwarding and latencyaware traffic splitting to reduce the consumption of flow entries and achieve load balancing. The evaluation results indicate that DFSM saves 15% to 30% of system flow entries in practical topologies and reduces the standard deviation of path latencies from 10% to 7% than do label-switched tunneling, and also reduces average latency by 10% to 48% by consuming 6% to 20% more flow entries than do ECMP in less-interconnected topologies. Note that the performance gain may not always be proportional to flow entry investment, with the interconnectivity between nodes being an important factor. The evaluation also indicates that per-flow provision consumes several times the flow entries consumed by DFSM but reduces latency by 10% at most. Besides, DFSM reduces the standard deviation of path latencies from 14% to 7% than do even traffic splitting. fault tolerance and reducing implementation costs. And for inter-DC networks, a large-scale cloud often connects multiple DCs via a wide area network (WAN). | Multipath routing: intra-DC vs inter-DCMany services in the cloud rely on low-latency DC interconnect (DCI) to enhance user experience (eg, streaming and web service); because of large and rapidly growing inter-DC traffic, traffic engineering (TE) methods are widely used to enhance inter-DC WAN performance. Multipath routing is a common way for TE; it, compared with single path routing, enhances bandwidth utilization and mitigates congestion. Traditional networks use Open Shortest Path First (OSPF). If there exists more than one shortest path between a node pair, the source node will split traffic into flows by a hash function and map the flows to these paths for transmission according to an equal-cost multipath (ECMP) mechanism. 3 For an intra-DC network with leaf-spine topology, the number of shortest paths between each leaf node pair is equal to the number of spine nodes in the network, and therefore, ECMP-based TE methods 4-7 are commonly used in intra-DC networks to improve the transmission performance for east-west traffic. However, the number of shortest paths between each node pair varies with irregular topologies, and applying ECMP on inter-DC WAN offers limited performance enhancement when there are few or ...