In networking, we rely on routing protocols to compute best path. That is to ask, from the perspective of a given router in a routing domain, what is the best way to reach a destination? Best path is typically computed using simplistic metrics like hop count, cost, bandwidth, and delay. Traditional “best path” thinking is effective, insofar as it goes. It scales to a large number of devices and destinations. It is resilient. It is mature. However, it has its limitations. Software defined WAN brings a much more sophisticated metric to the computation of best path.