Don't Panic - Network Time Protocol

Network Time Protocol, or NTP, is how computers agree on civil time without convening a committee every time a quartz oscillator develops opinions. A computer clock runs from an oscillator that is a little fast or slow. That error accumulates, and soon logs, certificates, jobs, and monitoring systems are telling slightly different stories about the same afternoon.

NTP does not grab a timestamp once and declare victory. It runs a feedback loop. A client asks time servers for measurements, estimates offset, the difference between its clock and a source, and delay, the time spent moving across the network. It rejects bad candidates, combines credible ones, then adjusts its own clock. The important verbs are measure, select, discipline, repeat. Everything else is the paperwork required to make those verbs less alarming.

The servers form a hierarchy. A reference clock supplies a primary server, called stratum 1. Secondary servers follow upstream servers, and clients can follow them in turn. Stratum counts synchronization steps, not moral worth. A lower number on a poor path can be less useful than a higher number backed by stable measurements. Several sources matter because one source cannot disagree with itself, which is a remarkably common limitation of single-source designs.

The surprise is that a reply is evidence, not proof. A server can answer packets while unsynchronized, inconsistent with the other sources, or reached through an unstable path. Basic NTP also does not authenticate the traffic. Network Time Security, or NTS, adds server authentication, packet integrity, replay protection, and request-response binding, but it cannot make a server honest or make network delay disappear. Timing remains a measurement problem with a security problem attached, because apparently one problem was not enough.

Leap seconds add policy rather than magic. NTP can signal a pending leap. Some services smear it by changing clock rate around the event. Mixing smeared and ordinary sources makes a client compare clocks that intentionally disagree, which is a poor basis for calm operations.

Read the Intro for the full architecture and security boundary. Open Slides for the four-timestamp exchange and the source-selection flow. Keep the Cheatsheet nearby when offset, jitter, stratum, root distance, or leap state needs interpretation. The Reference tab leads into the RFCs and implementation material once the mental model has stopped looking like a time-themed escape room.

Don't Panic - Network Time Protocol

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