Measuring the Practical Effect of DNS Root Server Instances: A China-Wide Case Study

DNS root servers are deployed using multiple globally distributed anycast instances, and the scale of instances across the globe has been rapidly growing. This paper presents a measurement study that investigates the practical effect of root server instances deployed in the Chinese mainland. Our analysis of this issue includes two-fold. First, we measure the catchment area of the root server instances and answer the question about which domestic networks are served. Our results show that some of the instances are not accessible from major ISP networks due to limits of BGP routing policies, and a number of root queries still turn to further instances outside the international gateway. Second, we evaluate the impact of deploying new instances on query performance and root server selection in resolvers. We confirm that root instances contribute to lowered query delay from networks within their catchment area. Through reviewing source code of mainstream DNS implementations, we find that less-latent root servers are generally preferred thus deploying root server instances increase their possibilities to absorb DNS root requests from nearby resolvers. We make recommendations to improve the operational status of the DNS root server system.