Most of current peer-to-peer designs build their own system overlays independent of the physical one. Nodes within unstructured systems form a random overlay, on the contrary, structured designs normally organize peers into an elegant identifier ring. However, all of those overlays are far from the physical one. Noticed that the system overlay is crucial for building a distributed system, this paper proposes to build system overlays based on the physical overlay. By making full use of physical network characteristics and taking advantages of both structured and unstructured protocols, a network-based peerto-peer system is built in this paper. Not only the system is highly efficient (the stretch is equal to one), but also it can adapt extremely system churning. The most important is that the maintenance overhead is very low, even under highly dynamic environment.