The so-called 'hierarchical' model is to divide the complex network design into several levels, each of which focuses on certain specifi c functions, which can make a complex big problem into many simple small problems. Hierarchical model can be applied to both LAN design and WAN design. In order to understand the importance of hierarchical design more clearly, it is best to understand the OSI (Open Systems Interconnection) reference model. The OSI model simplifies the communication requirements between computers. Similarly, the use of a hierarchical model to design a network can simplify the requirements of networking