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Load balancing large flows on multi-path networks

Peter Phaal of sFlow comments:

The graph in Figure 1 summarizes results from topologies with 2, 3 and 4 equal cost paths. For example, the Mininet topology in Figure 2 has two equal cost paths of 10Mbit/s (shown in blue and red). The iperf traffic generator was used to create a continuous stream of 20 second flows from h1 to h3 and from h2 to h4. If traffic were perfectly balanced, each flow would achieve 10Mbit/s throughput. However, Figure 1 shows that the throughput obtained using hash based ECMP load balancing is approximately 6.8Mbit/s. Interestingly, the average link throughput decreases as additional paths are added, dropping to approximately 6.2Mbit/s with four equal cost paths (see the blue bars in Figure 1).

Amazingly technical article about the impact of load balancing multiple “elephant” flows on multi path networks. Must read!

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Tom Hollingsworth

Tom Hollingsworth is a networking professional, blogger, and speaker on advanced technology topics. He is also an organizer for networking and wireless for Tech Field Day.  His blog can be found at

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