Two Days in the Life of the DNS Anycast Root Servers

The DNS root nameservers routinely use anycast in order to improve their service to clients and increase their resilience against various types of failures. We study DNS traffic collected over a two-day period in January 2006 at anycast instances for the C, F and K root nameservers. We analyze how anycast DNS service affects the worldwide population of Internet users. To determine whether clients actually use the instance closest to them, we examine client locations for each root instance, and the geographic distances between a server and its clients. We find that frequently the choice, which is entirely determined by BGP routing, is not the geographically closest one. We also consider specific AS paths and investigate some cases where local instances have a higher than usual proportion of non-local clients. We conclude that overall, anycast roots significantly localize DNS traffic, thereby improving DNS service to clients worldwide.