System Time And Date; Network Time Protocol - Dell S4048–ON Configuration Manual

System Time and Date

System 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
servers across different VRFs or the same VRF.

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 time and adjust the local clock accordingly. In addition, the message includes information to calculate the
expected timekeeping accuracy and reliability, as well as select the best from possibly several servers.
Following conventions established by the telephone industry [BEL86], the accuracy of each server is defined by a number called the
stratum, with the topmost level (primary servers) assigned as one and each level downwards (secondary servers) in the hierarchy
assigned as one greater than the preceding level.
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