Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 1008

55 System Time and Date System time and date settings are user-configurable and maintained through the network time protocol (NTP). System times and dates are also set in hardware settings using the Dell Networking OS CLI. Network Time Protocol The network time protocol (NTP) synchronizes timekeeping among a set of distributed time servers and clients. The protocol also coordinates time distribution in a large, diverse network with various interfaces. In NTP, servers maintain the time and NTP clients synchronize with a time-serving host. NTP clients choose from among several NTP servers to determine which offers the best available source of time and the most reliable transmission of information. NTP is a fault-tolerant protocol that automatically selects the best of several available time sources to synchronize to. You can combine multiple candidates to minimize the accumulated error. Temporarily or permanently insane time sources are detected and avoided. Dell Networking recommends configuring NTP for the most accurate time. In Dell Networking OS, you can configure other time sources (the hardware clock and the software clock). NTP is designed to produce three products: clock offset, roundtrip delay, and dispersion, all of which are relative to a selected reference clock. • Clock offset - represents the amount to adjust the local clock to bring it into correspondence with the reference clock. • Roundtrip delay - provides the capability to launch a message to arrive at the reference clock at a specified time. • Dispersion - represents the maximum error of the local clock relative to the reference clock. Because most host time servers synchronize via another peer time server, there are two components in each of these three products, those determined by the peer relative to the primary reference source of standard time and those measured by the host relative to the peer. In order to facilitate error control and management of the subnet itself, each of these components is maintained separately in the protocol. They provide not only precision measurements of offset and delay, but also definitive maximum error bounds, so that the user interface can determine not only the time, but the quality of the time as well. In what may be the most common client/server model, a client sends an NTP message to one or more servers and processes the replies as received. The server interchanges addresses and ports, overwrites certain fields in the message, recalculates the checksum and returns the message immediately. Information included in the NTP message allows the client to determine the server time regarding local 1008 System Time and Date