DNS is a critical component of the operation of Internet applications. However, DNS performance in the wide-area is not well understood. A number of studies present DNS performance measurements [1], [2], [3], [4], but the measurements are out of date, are not collected at client locations (e.g., they are taken at root servers), or are collected at very few client locations. In this paper we present the largest known study of widearea DNS performance at clients. We use data obtained under a

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... ty of network environments such as location in the Internet topology, connection technology and client ISP. We identify DNS system performance measures and investigate the degree to which they vary from site to site. We report on measures that are relatively consistent throughout the system such as the fraction of names whose lookups succeed, and those that vary widely, such as overall response times and response times from root and gTLD servers. We also discuss the impact of some of these measures on DNS performance for non-cached domain names, confirming some current notions about DNS operation while challenging others. Keywords-DNS, performance, active measurement. named, dig and gethostbyname() are provided with the Berkeley Internet Name Domain (BIND) software distribution.