A number of years ago I did some simulations and measurements to show how different DNS resolvers distribute their queries to a set of authoritative servers (see PAM 2004 paper and NANOG29 presentation). At that time I tested BIND, Windows, DJBDNS, and CNS. Recently someone asked if I know the behavior for PowerDNS. I ran a quick test against PowerDNS 3.1.7 that shows it having a strong affinity to a small number of authoritative servers. It seems to favor the nameservers with the lowest latency, which is not too surprising. In this case, it sent most of its queries to I- and F-roots, both of which are less than 1 ms away from the resolver host. (click for larger image)