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.@en

Time synchronization is crucial on the Internet, and the Network Time Protocol (NTP) serves as the primary synchronization protocol. The NTP Pool, a volunteer-driven project introduced 20 years ago, connects clients with NTP servers. Our analysis of Root DNS queries reveals the NTP Pool's widespread use as the most popular time service. Despite its popularity, there has been limited scrutiny of how NTP servers are assigned to clients. In this paper, we investigate the NTP Pool's DNS component (GeoDNS), which maps clients to servers, and find that the current algorithm is overly strict, creating unnecessary risks. We have shared our findings with the NTP Pool operators, who acknowledge them and plan to revise their algorithm to enhance security.@en