  Active DNS measurement is fundamental to understanding and improving the DNS
ecosystem. However, the absence of an extensible, high-performance, and
easy-to-use DNS toolkit has limited both the reproducibility and coverage of
DNS research. In this paper, we introduce ZDNS, a modular and open-source
active DNS measurement framework optimized for large-scale research studies of
DNS on the public Internet. We describe ZDNS' architecture, evaluate its
performance, and present two case studies that highlight how the tool can be
used to shed light on the operational complexities of DNS. We hope that ZDNS
will enable researchers to better -- and in a more reproducible manner --
understand Internet behavior.
