Data Center Network (DCN) is a popular approach to build a big and scalable network, which processed big data. One of the common topology used for DCN is Fat Tree, it is consists of a core switch, aggregation switch, and edge switch interconnecting with each other in a hierarchical manner. Each DCN topology includes Fat Tree, uses routing topology to make data transmission between each node in the network. DCN is a big network and so it is a good way to simulating some topology scheme in a simulator before implementing it to the real world. NS3 Simulator is the most widely used Network Simulator, well known for its discrete-event flexibility. In the paper, we present a framework for Fat Tree topology with XPath routing protocol in Network Simulator 3 (NS3). The information we provide includes performance evaluation of XPath routing protocol in Fat Tree DCN and tools available in NS3 to study routing protocol performance, the result shown that XPath routing protocol is better than default routing protocol for DCN running in NS3 simulator.