Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. It uses UDP port 123. NTP can maintain time to within 10 ms over the public internet. In operation since before 1985, NTP is one of the oldest Internet protocols in use. NTP was originally designed by David L. Mills of the University of Delaware, who still develops and maintains it with a team of volunteers.
For more about NTP click hereSome NTP Server commands are
ntpd
ntpq
ntptrace
ntpdc
NTP Server Scanner
PresenTense Time Server
PresenTense Time Client
PresenTense NTP Auditor
LAN Time Analyser
NTP Time Server Monitor
NTP Server Checker
NTP Server Monitor
Time watch
AtomSync
