Hack the Route Start free Open app Network services
NTP
Keeping clocks right by asking other clocks, in a hierarchy of strata from a reference clock down.
A client sends a UDP datagram to port 123 and, from four timestamps, computes its offset from the server and the round-trip delay. A reference clock (GPS, atomic) is stratum 1, a server following it stratum 2, and so on. A full client asks several servers and outvotes a falseticker; SNTP asks once and believes the answer. A wrong clock breaks what depends on time: TLS certificates (not yet valid, expired), one-time codes, Kerberos, the order of logs.