Deep Dive into NTP Pool's Popularity and Mapping

Giovane C. M. Moura, Marco Davids, Caspar Schutijser, Cristian Hesselman, John Heidemann, Georgios Smaragdakis

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Time synchronization is of paramount importance on the Internet, with the Network Time Protocol (NTP) serving as the primary synchronization protocol. The NTP Pool, a volunteer-driven initiative launched two decades ago, facilitates connections between clients and NTP servers. Our analysis of root DNS queries reveals that the NTP Pool has consistently been the most popular time service. We further investigate the DNS component (GeoDNS) of the NTP Pool, which is responsible for mapping clients to servers. Our findings indicate that the current algorithm is heavily skewed, leading to the emergence of time monopolies for entire countries. For instance, clients in the US are served by 551 NTP servers, while clients in Cameroon and Nigeria are served by only one and two servers, respectively, out of the 4k+ servers available in the NTP Pool. We examine the underlying assumption behind GeoDNS for these mappings and discover that time servers located far away can still provide accurate clock time information to clients. We have shared our findings with the NTP Pool operators, who acknowledge them and plan to revise their algorithm to enhance security.
Original languageEnglish
Article number15
Number of pages30
JournalProceedings of the ACM on Measurement and Analysis of Computing Systems
Issue number1
Publication statusPublished - 2024
EventACM SIGMETRICS/Performance 2024 conference - Venice, Italy
Duration: 10 Jun 202414 Jun 2024


  • NTP
  • NTPPool
  • DNS
  • Measurements
  • Clientmapping


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