NTP synchronizes the internal clocks of various network devices across large, diverse networks to universal standard time. NTP protocol runs over the User Datagram Protocol (UDP), which in turn runs over IP.
The NTPv3 specification is documented in RFC 1305 and supports IPv4 addresses.
Note
NTPv3 is only supported on VSP 8600 Series.
The NTPv4 specification is documented in RFC 5905 and supports both IPv4 and IPv6 addresses.
Every network device relies on an internal system clock to maintain accurate time. On local devices, the internal system clock is typically manually set 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 adjusts the time of the devices so that they synchronize within a millisecond (ms) on LANs and up to a few tens of milliseconds on WANs relative to Coordinated Universal Time (UTC).
The NTP client on the switch supports only unicast client mode. In this mode, the NTP client sends NTP time requests to other remote time servers in an asynchronous fashion. The NTP client collects four samples of time from each remote time server. A clock selection algorithm determines the best server among the selected samples based on stratum, delay, dispersion and the last updated time of the remote server. The real time clock (RTC) is adjusted to the selected sample from the chosen server.
A peer is a device that runs NTP software. However, this implementation of NTP refers to peers as remote time servers that provide time information to other time servers on the network and to the local NTP client. An NTP client refers to the local network device, the switch, that accepts time information from other remote time servers.