We surveyed the latency of upper DNS hierarchy from 19593 vantage points around the world to investigate the impact of uneven distribution of top level DNS servers on end-user latency. Our findings included: 1) generally top level DNS servers served Internet users efficiently, with median latency 20.26ms for root, 42.64ms for .com/.net, 39.07ms for .org; 2) quality of service was uneven, Europe and North America were the best while Africa and South America were 3 to 6 times worse; 3) most of the root servers performed well in Europe and North America, but only F, J, L roots showed low query latency in other continents; 4) query latency of F and L roots showed that only about 60 resolvers were routed to the nearest anycast instances. We also revealed two problems that lead to constantly large query latency (6s~18s) for resolvers. One was buggy implementation of some resolvers on IPv4/IPv6 dual-stack hosts, the other was misconfigured middle-boxes that filtered large or fragmented DNSSEC packets.
['Jinjin Liang', 'Jian Jiang', 'Haixin Duan', 'Kang Li', 'Jianping Wu']
Measuring query latency of top level DNS servers