Abstract: A fundamental goal of data-center networking is to efficiently interconnect a large number of servers with low equipment cost while keeping high network bandwidth. The traditional tree-based networking schemes were born with the performance bottleneck and extensibility problems. To tackle the problems, some server-centric data center networking structures have been proposed. However, they are not truly expandable and suffer a low degree of regularity and symmetry. Since servers generally have two network interface card ports, how to design a high extensible and cost-effective data center networking structure with high performance based on servers’ two network interface card ports and without expensive high-end switches is a challenging problem. This paper proposes a high extensible modular server-centric data center networking structure called DCent, which requires that servers have two network interface card ports and only use commodity off-the-shelf mini-switches. We also develop low-overhead and robust routing schemes for DCent. Mathematical analysis shows that DCent has excellent topology properties. Although the server degree is only 2, DCent can be expanded very easily to encompass hundreds of thousands servers with the low diameter and high bisection width. DCent also has fine modularity where servers interconnect by switches which avoids direct connection between servers.