Greenfield deployment

A greenfield deployment, or building a network from scratch, is perhaps the easiest in terms of co-exist an SDN OpenFlow network with traditional network. The only interaction between your SDN network to traditional network equipment will almost only be at the edge, which in today's world, almost always uses BGP as the exchange protocol. Your external facing node will be using BGP, such as what we have seen with the Ryu BGP library, while internally you are free to use any type of connectivity and topology you wish. If you already have a way to isolate your datacenter network with this approach, in the case of a greenfield deployment you can use the same method. If you use a bottom up approach, you can start by calculating the amount of compute resource you need, tally it up to the number of racks, and determine the number of top of rack switches as a starting point. Then calculate the number of over subscription, if any, at each of the aggregation layers, leaves, spines...