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Network Time Protocol (NTP) synchronizes the internal clocks of various network devices across large, diverse networks to universal standard time. NTP runs over UDP, which in turn runs over IP. The NTP protocol specification is documented in RFC 1305.
Every network device relies on an internal system clock to maintain accurate time. On local devices, the internal system clock is usually set by eye or by wristwatch to within a minute or two of the actual time and is rarely reset at regular intervals. Many local clocks are battery-backed devices that use room temperature clock oscillators that can drift as much as several seconds each day. NTP solves this problem by automatically adjusting the time of the devices so that they are synchronized within a millisecond (ms) on LANs and up to a few tens of milliseconds on WANs relative to Coordinated Universal Time (UTC).
The current implementation of NTP supports only unicast client mode.
For more information about NTP, see Networking Concepts for the Passport 8000 Series Switch.