Network Time Protocol

Network Time Protocol (NTP) is a protocol built on top of TCP/IP that assures accurate local timekeeping by referring to Network Time Servers located on the Internet. This protocol allows local clocks to be synchronized with radio, atomic, or other reference clocks within milliseconds over long time periods.

History

 * NTPv0 was defined in 958 and implemented in Unix in 1985.
 * NTPv1 was defined in RFC 1059 in 1988.
 * NTPv2 was defined in RFC 1119 in 1989.
 * NTPv3 was defined in RFC 1305 in 1991, but still relied on a 64-bit date value which would expire in 2036. This implementation was first adopted by the Date & Time control panel of Mac OS 8.5 in October 1998.
 * The last proposed specification for NTPv4 was published in RFC 5905 in 2010. It addressed the date limitation by adopting a 128-bit value. Due to security concerns, Apple no longer relies on NTP as of macOS Mojave (10.14) in 2018 and instead implemented its own timed function.