Abstract: Due to the rapid development of cloud computing, the demand of Internet service providers for data centers is increasing rapidly. As a key technology of data center networks, routing is responsible for selecting routes for network traffic within or across data centers. It can also provide diffe- rential services for traffic with different QoS (Quality of Service) requirements. However, for large-scale data centers, due to the unpredictable traffic of applications and the topology characteristic of data centers, the traditional routing methods in the Internet cannot provide satisfactory high throughput and resource utilization. Network congestion make it hard to provide guaranteed bandwidth or transmission delay for flows with the demand of QoS. This paper classifies and compares the routing problems in data centers, and then emphatically introduces the research progress about the unicast routing methods. Further, the congestion-aware routing methods are introduced. Finally, the routing technology of the new data center networks is discussed.

Key words: data center network, routing protocol, congestion control, joint optimization