Till now, we’ve already learned how a fat tree topology can help introduce flexibility into data centers and lower the cost on high-end device. From the programming aspect, we’ve learned use mininet to simulate a virtual network and implement an OpenFlow controller with Ryu in python. However, there are still many successful studies on data center network. One of them is the famous Portland system, which may be implemented in the following articles. Besides, to introduce traffic engineering into Portland system, we may also use some Layer 3 strategy.