Administrator Guide
System Time and Date
System time and date settings are user-congurable and maintained through the network time protocol (NTP).
System times and dates are also set in hardware settings using the Dell Networking OS CLI.
Topics:
• Network Time Protocol
• Time and Date
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 oers 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 conguring NTP for the most accurate time. In Dell Networking OS, you can congure other time sources
(the hardware clock and the software clock).
NTP is designed to produce three products: clock oset, roundtrip delay, and dispersion, all of which are relative to a selected reference
clock.
• Clock oset — 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 specied 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 oset and delay, but also denitive 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 elds 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 dened 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.
Dell Networking OS synchronizes with a time-serving host to get the correct time. You can set Dell Networking OS to poll specic NTP
time-serving hosts for the current time. From those time-serving hosts, the system chooses one NTP host with which to synchronize and
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