2000-03-29 16:38:44 +04:00
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The Network Time Protocol (NTP) Distribution
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</title></head><body><h3>
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The Network Time Protocol (NTP) Distribution
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</h3>
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<H4>Introduction</H4>
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Note: The software contained in this distribution is available without
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charge under the conditions set forth in the <A
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HREF=copyright.htm>Copyright Notice</A>.
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<P>The Network Time Protocol (NTP) is used to synchronize the time of a
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computer client or server to another server or reference time source,
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such as a radio or satellite receiver or modem. It provides client
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accuracies typically within a millisecond on LANs and up to a few tens
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of milliseconds on WANs relative to a primary server synchronized to
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Coordinated Universal Time (UTC) via a Global Positioning Service (GPS)
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receiver, for example. Typical NTP configurations utilize multiple
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redundant servers and diverse network paths, in order to achieve high
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accuracy and reliability. Some configurations include cryptographic
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authentication to prevent accidental or malicious protocol attacks.
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<P>Background information on computer network time synchronization can
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be found on the <A HREF=exec.htm>Executive Summary - Computer Network
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Time Synchronization</A> page. Discussion on protocol conformance issues
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and interoperability with previous NTP versions can be found in the <A
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HREF=biblio.htm>Protocol Conformance Statement</A> page. Discussion on
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year-2000 issues can be found in the <A HREF=y2k.htm>Year 2000
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Conformance Statement page</A>. Background information, bibliography and
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briefing slides suitable for presentations can be found in the <A
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HREF=http://www.eecis.udel.edu/~mills/ntp.htm> Network Time
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Synchronization Project</A> page.
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<H4>Building and Installing NTP</H4>
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The <A HREF=build.htm>Building and Installing the Distribution
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</A>page presents an overview of the procedures for compiling the
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distribution and installing it on a typical client or server. The build
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procedures inspect the system hardware and software environment and
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automatically select the appropriate options for that environment. While
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these procedures work with most computers and operating systems marketed
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today, exceptions requiring manual intervention do exist, as documented
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in the <A HREF=config.htm>Configuration Options </A>and <A
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HREF=release.htm>Release Notes </A>pages.
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<P>Bringing up a NTP primary server requires a radio or satellite
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receiver or modem. The distribution includes hardware drivers for over
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two dozen radio clocks and modem services. A list of the particular
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receivers and modem drivers supported in the distribution is given in
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the <A HREF=refclock.htm>Reference Clock Drivers </A>page. For most
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popular workstations marketed by Digital, Sun and Hewlett Packard, as
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well as widely available Unix clones such as FreeBSD and Linux, the
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automatic build procedures select all drivers that run on the target
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machine. While this increases the size of the executable binary
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somewhat, individual drivers can be included or excluded using the
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configure utility documented in the Configuration Options page.
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<H4>Configuring Clients and Servers</H4>
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<p>NTP is by its very nature a complex distributed network application
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and can be configured and used for a great many widely divergent
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timekeeping scenarios. The documentation presented on these pages
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attempts to cover the entire suite of configuration, operation and
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maintenance facilities which this distribution supports. However, most
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applications will need only a few of these facilities. If this is the
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case, the <a href=quick.htm>Quick Start</a> page may be useful to get a
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simple workstation on the air with an existing server.
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<p>However, in order to participate in the existing NTP synchronization
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subnet and obtain accurate, reliable time, it is usually necessary to
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construct an appropriate configuration file, commonly called
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<TT>ntp.conf</TT>, which establishes the servers and/or external
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receivers or modems to be used by this particular machine. Directions
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for constructing this file are in the <A HREF=notes.htm>Notes on
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Configuring NTP and Setting up a NTP Subnet </A>page. However, in many
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common cases involving simple network topologies and workstations, the
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file data can be specified entirely on the command line.
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<P>The most important factor in providing accurate, reliable time is the
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selection of modes and servers to be used in the configuration file. NTP
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support for one or more computers is normally engineered as part of the
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existing NTP synchronization subnet. The existing NTP subnet consists of
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a multiply redundant hierarchy of servers and clients, with each level
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in the hierarchy identified by stratum number. Primary servers operate
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at stratum one and provide synchronization to secondary servers
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operating at stratum two and so on to higher strata. In this hierarchy,
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clients are simply servers that have no dependents.
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<P>The NTP subnet in early 1998 includes 70 public primary (stratum 1)
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servers synchronized directly to UTC by radio, satellite or modem and
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located in every continent of the globe, except Antarctica (soon).
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Normally, client workstations and servers with a relatively small number
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of clients do not synchronize to primary servers. There are 106 public
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secondary (stratum 2) servers synchronized to the primary servers and
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providing synchronization to a total in excess of 100,000 clients and
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servers in the Internet. The current lists are maintained in the <A
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HREF=http://www.eecis.udel.edu/~mills/ntp/index.htm>Information on Time
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and Frequency Services</A> page, which is updated frequently. There are
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numerous private primary and secondary servers not normally available to
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the public as well. You are strongly discouraged from using these
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servers, since they sometimes hide in little ghettos behind dinky links
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to the outside world and your traffic can bring up expensive ISDN lines,
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causing much grief and frustration.
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<H4>Resolving Problems</H4>
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Like other things Internet, the NTP synchronization subnets tend to be
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large and devilishly intricate, with many opportunities for
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misconfiguration and network problems. The NTP engineering model is
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specifically designed to help isolate and repair such problems using an
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integrated management protocol, together with a suite of monitoring and
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debugging tools. There is an optional data recording facility which can
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be used to record normal and aberrant operation, log problems to the
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system log facility, and retain records of client access. The <A
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HREF=debug.htm>NTP Debugging Techniques </A>and <A
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HREF=hints.htm>Hints and Kinks </A>pages contain useful information
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for identifying problems and devising solutions.
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<P>Users are requested to report bugs, offer suggestions and contribute
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additions to this distribution. The <A HREF=patches.htm>Patching
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Procedures </A>page suggests procedures which greatly simplify
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distribution updates, while the <A HREF=porting.htm>Porting Hints
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</A>page suggest ways to make porting this code to new hardware and
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operating systems easier. Additional information on reference clock
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driver construction and debugging can be found in the <A
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HREF=refclock.htm>Reference Clock Drivers </A>page. Further
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information on NTP in the Internet can be found in the <A
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HREF=http://www.eecis.udel.edu/~ntp>NTP
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web page</A>.
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<H4>Program Manual Pages</H4>
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<ul>
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<li><A HREF=ntpd.htm><TT>ntpd</TT> - Network Time Protocol (NTP)
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daemon</A></LI>
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<LI><A HREF=ntpq.htm><TT>ntpq</TT> - standard NTP query
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program</A></LI>
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<LI><A HREF=ntpdc.htm><TT>ntpdc</TT> - special NTP query
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program</A></LI>
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<LI><A HREF=ntpdate.htm><TT>ntpdate</TT> - set the date and time via
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NTP</A></LI>
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<LI><A HREF=ntptrace.htm><TT>ntptrace</TT> - trace a chain of NTP
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servers back to the primary source</A></LI>
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<LI><A HREF=tickadj.htm><TT>tickadj</TT> - set time-related kernel
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variables</A></LI>
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<LI><A HREF=ntptime.htm><TT>ntptime</TT> - read kernel time
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variables</A></LI>
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2000-04-22 18:51:59 +04:00
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<LI><A HREF=genkeys.htm><TT>ntp_genkeys</TT> - generate public and
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private keys</A></LI>
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2000-03-29 16:38:44 +04:00
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</ul>
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<H4>Supporting Documentation</H4>
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<ul>
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<LI<A HREF=ntp.htm>NTP Reference Library</A></LI>
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<LI><A HREF=copyright.htm>Copyright Notice</A></LI>
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<LI><A HREF=exec.htm>Executive Summary - Computer Network Time
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Synchronization</A></LI>
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<LI><A HREF=biblio.htm>Protocol Conformance Statement</A></LI>
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<LI><A HREF=y2k.htm>Year 2000 Conformance Statement</A></LI>
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<LI><A HREF=notes.htm>Notes on Configuring NTP and Setting up a NTP
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Subnet</A></LI>
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<LI><A HREF=release.htm>NTP Version 4 Release Notes</A></LI>
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<LI><A HREF=build.htm>Building and Installing the
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Distribution</A></LI>
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<LI><A HREF=config.htm>Configuration Options</A></LI>
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<LI><A HREF=debug.htm>NTP Debugging Techniques</A></LI>
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<LI><A HREF=refclock.htm>Reference Clock Drivers</A></LI>
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<LI><A HREF=patches.htm>Patching Procedures</A></LI>
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<LI><A HREF=hints.htm>Hints and Kinks</A></LI>
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<LI><A HREF=porting.htm>Porting Hints</A></LI>
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</ul>
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<H4>Application Notes</H4>
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<ul>
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<LI><A HREF=prefer.htm>Mitigation Rules and the <TT>prefer</TT>
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Keyword</A></LI>
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<LI><A HREF=assoc.htm>Association Management</A></LI>
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<LI><A HREF=pps.htm>Pulse-per-second (PPS) Signal Interfacing</A></LI>
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<LI><A HREF=gadget.htm>Gadget Box PPS Level Converter and CHU
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Modem</A></LI>
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<LI><A HREF=measure.htm>Time and Time Interval Measurement with
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Application to Computer and Network Performance Evaluation</A></LI>
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<LI><A HREF=kern.htm>A Kernel Model for Precision Timekeeping</A></LI>
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<LI><A HREF=kernpps.htm>A Kernel Programming Interface for Precision
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Time Signals</A></LI>
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</ul>
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2000-04-22 20:46:49 +04:00
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<hr><a href=index.htm>Home</a><address><a
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href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a>
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</address></a></body></html>
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