System Time and DateSystem time and date settings and the network time protocol (NTP) are supported on Dell Networking OS.You can set system times and dates and maintained through the NTP. They are also set through the Dell Networking Operating System(OS) command line interfaces (CLIs) and hardware settings.The Dell Networking OS supports reaching an NTP server through different VRFs. You can configure a maximum of eight logging serversacross different VRFs or the same VRF.Topics:• Network Time Protocol• Dell Networking OS Time and DateNetwork Time ProtocolThe 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 andNTP clients synchronize with a time-serving host. NTP clients choose from among several NTP servers to determine which offers the bestavailable 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 combinemultiple 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 referenceclock.• 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 thepeer.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 candetermine 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 asreceived. The server interchanges addresses and ports, overwrites certain fields in the message, recalculates the checksum and returns themessage immediately. Information included in the NTP message allows the client to determine the server time regarding local time andadjust the local clock accordingly. In addition, the message includes information to calculate the expected timekeeping accuracy andreliability, as well as select the best from possibly several servers.56System Time and Date 945
