Data centers have become increasingly essential part of Internet communications, thus there have been interest in understanding how to better design and manage data centers. In this paper, the authors explain a typical data center network architecture in the industry, the challenges modern data center networks encounter today and introduce proposed solutions by a recent research. Typical data center network architecture usually consists of switches and routers in two- or three-level hierarchy. It is an instance of three-level design. The following explanation for the figure is based on the papers. The figure contains hierarchy of top layer core routers on the top connecting to the servers in racks at the bottom.