Which algorithm does NTP use to select accurate time servers?

Which algorithm does NTP use to select accurate time servers?

• A. The random algorithm
• B. The intersection algorithm, a modified version of Marzullo's algorithm
• C. The BCP algorithm
• D. The Dijkstra algorithm

Answer: (D)

NTP uses a consensus-based approach to choose accurate time sources by comparing the offsets and delays reported by multiple servers and looking for agreement among them. Each server’s time, with its associated uncertainty, is represented as an interval. The algorithm then seeks the largest set of intervals that overlap, meaning those servers agree within their error bounds. This intersection-based method is a modified version of Marzullo’s algorithm and is designed to identify a trustworthy cluster of time sources. Once a consistent set is found, NTP can select the best among them or combine them to form a stable time reference. Dijkstra’s algorithm, by contrast, is a shortest-path algorithm used for routing and graph traversal, not for evaluating time sources. That’s why it doesn’t apply to how NTP selects accurate servers.

NTP uses a consensus-based approach to choose accurate time sources by comparing the offsets and delays reported by multiple servers and looking for agreement among them. Each server’s time, with its associated uncertainty, is represented as an interval. The algorithm then seeks the largest set of intervals that overlap, meaning those servers agree within their error bounds. This intersection-based method is a modified version of Marzullo’s algorithm and is designed to identify a trustworthy cluster of time sources. Once a consistent set is found, NTP can select the best among them or combine them to form a stable time reference.

Dijkstra’s algorithm, by contrast, is a shortest-path algorithm used for routing and graph traversal, not for evaluating time sources. That’s why it doesn’t apply to how NTP selects accurate servers.