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| 5 | <title>The Network Time Protocol (NTP) Distribution</title> |
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| 6 | </head> |
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| 7 | <body> |
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| 8 | <h3>The Network Time Protocol (NTP) Distribution</h3> |
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| 9 | |
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| 10 | <img align="left" src="pic/barnstable.gif" alt="gif"><a href= |
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| 11 | "http://www.eecis.udel.edu/~mills/pictures.htm"><i>P.T. Bridgeport |
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| 12 | Bear</i>; from <i>Pogo</i>, Walt Kelly</a> |
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| 13 | |
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| 14 | <p>Pleased to meet you.<br clear="left"> |
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| 15 | </p> |
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| 16 | |
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| 17 | <hr> |
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| 18 | <h4>Introduction</h4> |
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| 19 | |
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| 20 | Note: The software contained in this distribution is available |
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| 21 | without charge under the conditions set forth in the <a href= |
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| 22 | "copyright.htm">Copyright Notice</a>. |
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| 23 | |
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| 24 | <p>The Network Time Protocol (NTP) is used to synchronize the time |
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| 25 | of a computer client or server to another server or reference time |
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| 26 | source, such as a radio or satellite receiver or modem. It provides |
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| 27 | accuracies typically within a millisecond on LANs and up to a few |
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| 28 | tens of milliseconds on WANs relative to Coordinated Universal Time |
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| 29 | (UTC) via a Global Positioning Service (GPS) receiver, for example. |
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| 30 | Typical NTP configurations utilize multiple redundant servers and |
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| 31 | diverse network paths in order to achieve high accuracy and |
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| 32 | reliability. Some configurations include cryptographic |
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| 33 | authentication to prevent accidental or malicious protocol attacks |
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| 34 | and some provide automatic server discovery using IP multicast.</p> |
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| 35 | |
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| 36 | <p>Background information on computer network time synchronization |
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| 37 | can be found on the <a href="exec.htm">Executive Summary - Computer |
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| 38 | Network Time Synchronization</a> page. Discussion on protocol |
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| 39 | conformance issues and interoperability with previous NTP versions |
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| 40 | can be found in the <a href="biblio.htm">Protocol Conformance |
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| 41 | Statement</a> page. Discussion on how NTP reckons the time can be |
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| 42 | found in the <a href="leap.htm">NTP Timescale and Leap Seconds</a> |
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| 43 | page. Background information, bibliography and briefing slides |
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| 44 | suitable for presentations can be found in the <a href= |
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| 45 | "http://www.eecis.udel.edu/~mills/ntp.htm">Network Time |
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| 46 | Synchronization Project</a> page. Additional information can be |
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| 47 | found at the NTP web site <a href="http://www.ntp.org"> |
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| 48 | www.ntp.org</a>. Please send bug reports to <a href= |
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| 49 | "mailto:bugs@mail.ntp.org"><bugs@mail.ntp.org></a>.</p> |
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| 50 | |
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| 51 | <h4>Building and Installing NTP</h4> |
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| 52 | |
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| 53 | NTP supports Unix and Windows (NT4 and 2000) systems. The <a href= |
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| 54 | "build.htm">Building and Installing the Distribution</a> page |
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| 55 | presents an overview of the procedures for compiling the |
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| 56 | distribution and installing it on a typical client or server. The |
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| 57 | build procedures inspect the system hardware and software |
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| 58 | environment and automatically select the appropriate options for |
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| 59 | that environment. While these procedures work with most computers |
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| 60 | and operating systems marketed today, exceptions requiring manual |
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| 61 | intervention do exist, as documented in the <a href="config.htm"> |
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| 62 | Configuration Options</a> and <a href="release.htm">Release |
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| 63 | Notes</a> pages. Note that support for strong cryptography requires |
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| 64 | cryptographic libraries not included in this distribution. |
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| 65 | |
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| 66 | <p>Bringing up a NTP primary server requires a radio or satellite |
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| 67 | receiver or modem. It is also possible to configure a machine on an |
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| 68 | isolated network with the local clock driver and have other |
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| 69 | machines synchronize to it. The distribution includes hardware |
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| 70 | drivers for the local clock and over three dozen radio clocks and |
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| 71 | modem services. A list of supported drivers is given in the <a |
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| 72 | href="refclock.htm">Reference Clock Drivers</a> page. For most |
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| 73 | popular workstations marketed by Digital/Compaq, Sun and Hewlett |
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| 74 | Packard, as well as widely available Unix clones such as FreeBSD |
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| 75 | and Linux, the automatic build procedures select all drivers that |
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| 76 | run on the target machine. While this increases the size of the |
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| 77 | executable binary somewhat, individual drivers can be included or |
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| 78 | excluded using the configure utility documented in the |
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| 79 | Configuration Options page.</p> |
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| 80 | |
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| 81 | <h4>Configuring Clients and Servers</h4> |
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| 82 | |
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| 83 | <p>NTP is by its very nature a complex distributed network |
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| 84 | application and can be configured and used for a great many widely |
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| 85 | divergent timekeeping scenarios. The documentation presented on |
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| 86 | these pages attempts to cover the entire suite of configuration, |
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| 87 | operation and maintenance facilities which this distribution |
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| 88 | supports. However, most applications will need only a few of these |
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| 89 | facilities. If this is the case, the <a href="quick.htm">Quick |
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| 90 | Start</a> page may be useful to get a simple workstation on the air |
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| 91 | with an existing server.</p> |
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| 92 | |
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| 93 | <p>However, in order to participate in the existing NTP |
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| 94 | synchronization subnet and obtain accurate, reliable time, it is |
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| 95 | usually necessary to construct an appropriate configuration file, |
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| 96 | commonly called <tt>ntp.conf</tt>, which establishes the servers |
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| 97 | and/or external receivers or modems to be used by this particular |
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| 98 | machine. Directions for constructing this file are in the <a href= |
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| 99 | "notes.htm">Notes on Configuring NTP and Setting up a NTP |
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| 100 | Subnet</a> page. However, in many common cases involving simple |
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| 101 | network topologies and workstations, the configuration data can be |
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| 102 | specified entirely on the command line for the <a href="ntpd.htm"> |
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| 103 | <tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a>.</p> |
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| 104 | |
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| 105 | <p>The most important factor in providing accurate, reliable time |
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| 106 | is the selection of modes and servers to be used in the |
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| 107 | configuration file. A discussion on the available modes is on the |
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| 108 | <a href="assoc.htm">Association Management</a> page. NTP support |
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| 109 | for one or more computers is normally engineered as part of the |
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| 110 | existing NTP synchronization subnet. The existing NTP subnet |
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| 111 | consists of a multiply redundant hierarchy of servers and clients, |
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| 112 | with each level in the hierarchy identified by stratum number. |
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| 113 | Primary servers operate at stratum one and provide synchronization |
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| 114 | to secondary servers operating at stratum two and so on to higher |
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| 115 | strata. In this hierarchy, clients are simply servers that have no |
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| 116 | dependents.</p> |
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| 117 | |
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| 118 | <p>The NTP subnet in late 2000 includes over a hundred public |
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| 119 | primary (stratum 1) servers synchronized directly to UTC by radio, |
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| 120 | satellite or modem and located in every continent of the globe, |
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| 121 | including Antarctica. Normally, client workstations and servers |
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| 122 | with a relatively small number of clients do not synchronize to |
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| 123 | primary servers. There are over a hundred public secondary (stratum |
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| 124 | 2) servers synchronized to the primary servers and providing |
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| 125 | synchronization to a total in excess of 100,000 clients and servers |
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| 126 | in the Internet. The current lists are maintained in the <a href= |
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| 127 | "http://www.eecis.udel.edu/~mills/ntp/index.htm">Information on |
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| 128 | Time and Frequency Services</a> page, which is updated frequently. |
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| 129 | There are numerous private primary and secondary servers not |
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| 130 | normally available to the public as well. You are strongly |
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| 131 | discouraged from using these servers, since they sometimes hide in |
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| 132 | little ghettos behind dinky links to the outside world and your |
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| 133 | traffic can bring up expensive ISDN lines, causing much grief and |
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| 134 | frustration.</p> |
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| 135 | |
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| 136 | <h4>Resolving Problems</h4> |
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| 137 | |
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| 138 | Like other things Internet, the NTP synchronization subnets tend to |
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| 139 | be large and devilishly intricate, with many opportunities for |
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| 140 | misconfiguration and network problems. The NTP engineering model is |
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| 141 | specifically designed to help isolate and repair such problems |
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| 142 | using an integrated management protocol, together with a suite of |
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| 143 | monitoring and debugging tools. There is an optional data recording |
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| 144 | facility which can be used to record normal and aberrant operation, |
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| 145 | log problems to the system log facility, and retain records of |
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| 146 | client access. The <a href="debug.htm">NTP Debugging Techniques</a> |
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| 147 | and <a href="hints.htm">Hints and Kinks</a> pages contain useful |
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| 148 | information for identifying problems and devising solutions. |
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| 149 | |
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| 150 | <p>Users are requested to report bugs, offer suggestions and |
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| 151 | contribute additions to this distribution. The <a href= |
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| 152 | "patches.htm">Patching Procedures</a> page suggests procedures |
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| 153 | which greatly simplify distribution updates, while the <a href= |
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| 154 | "porting.htm">Porting Hints</a> page suggest ways to make porting |
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| 155 | this code to new hardware and operating systems easier. Additional |
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| 156 | information on reference clock driver construction and debugging |
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| 157 | can be found in the <a href="refclock.htm">Reference Clock |
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| 158 | Drivers</a> page. Further information on NTP in the Internet can be |
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| 159 | found in the <a href="http://www.eecis.udel.edu/~ntp">NTP web |
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| 160 | page</a>.</p> |
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| 161 | |
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| 162 | <h4>Program Manual Pages</h4> |
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| 163 | |
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| 164 | <ul> |
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| 165 | <li><a href="ntpd.htm"><tt>ntpd</tt> - Network Time Protocol (NTP) |
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| 166 | daemon</a></li> |
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| 167 | |
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| 168 | <li><a href="ntpq.htm"><tt>ntpq</tt> - standard NTP query |
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| 169 | program</a></li> |
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| 170 | |
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| 171 | <li><a href="ntpdc.htm"><tt>ntpdc</tt> - special NTP query |
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| 172 | program</a></li> |
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| 173 | |
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| 174 | <li><a href="ntpdate.htm"><tt>ntpdate</tt> - set the date and time |
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| 175 | via NTP</a></li> |
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| 176 | |
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| 177 | <li><a href="ntptrace.htm"><tt>ntptrace</tt> - trace a chain of NTP |
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| 178 | servers back to the primary source</a></li> |
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| 179 | |
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| 180 | <li><a href="tickadj.htm"><tt>tickadj</tt> - set time-related |
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| 181 | kernel variables</a></li> |
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| 182 | |
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| 183 | <li><a href="ntptime.htm"><tt>ntptime</tt> - read kernel time |
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| 184 | variables</a></li> |
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| 185 | |
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| 186 | <li><a href="genkeys.htm"><tt>ntp-genkeys</tt> - generate public |
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| 187 | and private keys</a></li> |
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| 188 | </ul> |
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| 189 | |
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| 190 | <h4>Supporting Documentation</h4> |
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| 191 | |
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| 192 | <ul> |
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| 193 | <li><a href="http://www.eecis.udel.edu/~mills/ntp.htm">NTP Project |
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| 194 | and Reference Library</a></li> |
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| 195 | |
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| 196 | <li><a href="copyright.htm">Copyright Notice</a></li> |
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| 197 | |
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| 198 | <li><a href="exec.htm">Executive Summary - Computer Network Time |
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| 199 | Synchronization</a></li> |
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| 200 | |
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| 201 | <li><a href="biblio.htm">Protocol Conformance Statement</a></li> |
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| 202 | |
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| 203 | <li><a href="leap.htm">NTP Timescale and Leap Seconds</a></li> |
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| 204 | |
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| 205 | <li><a href="notes.htm">Notes on Configuring NTP and Setting up a |
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| 206 | NTP Subnet</a></li> |
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| 207 | |
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| 208 | <li><a href="release.htm">NTP Version 4 Release Notes</a></li> |
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| 209 | |
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| 210 | <li><a href="build.htm">Building and Installing the |
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| 211 | Distribution</a></li> |
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| 212 | |
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| 213 | <li><a href="config.htm">Configuration Options</a></li> |
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| 214 | |
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| 215 | <li><a href="debug.htm">NTP Debugging Techniques</a></li> |
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| 216 | |
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| 217 | <li><a href="refclock.htm">Reference Clock Drivers</a></li> |
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| 218 | |
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| 219 | <li><a href="patches.htm">Patching Procedures</a></li> |
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| 220 | |
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| 221 | <li><a href="hints.htm">Hints and Kinks</a></li> |
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| 222 | |
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| 223 | <li><a href="porting.htm">Porting Hints</a></li> |
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| 224 | </ul> |
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| 225 | |
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| 226 | <h4>Application Notes</h4> |
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| 227 | |
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| 228 | <ul> |
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| 229 | <li><a href="prefer.htm">Mitigation Rules and the <tt>prefer</tt> |
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| 230 | Keyword</a></li> |
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| 231 | |
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| 232 | <li><a href="assoc.htm">Association Management</a></li> |
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| 233 | |
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| 234 | <li><a href="pps.htm">Pulse-per-second (PPS) Signal |
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| 235 | Interfacing</a></li> |
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| 236 | |
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| 237 | <li><a href="gadget.htm">Gadget Box PPS Level Converter and CHU |
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| 238 | Modem</a></li> |
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| 239 | |
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| 240 | <li><a href="measure.htm">Time and Time Interval Measurement with |
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| 241 | Application to Computer and Network Performance Evaluation</a></li> |
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| 242 | |
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| 243 | <li><a href="kern.htm">Kernel Model for Precision |
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| 244 | Timekeeping</a></li> |
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| 245 | |
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| 246 | <li><a href="kernpps.htm">Kernel Programming Interface for |
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| 247 | Precision Time Signals</a></li> |
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| 248 | </ul> |
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| 249 | |
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| 250 | <hr> |
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| 251 | <center><img src="pic/pogo1a.gif" alt="gif"></center> |
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| 252 | |
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| 253 | <br> |
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| 254 | <a href="index.htm"><img align="left" src="pic/home.gif" alt= |
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| 255 | "gif"></a> |
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| 256 | |
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| 257 | <address><a href="mailto:mills@udel.edu">David L. Mills |
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| 258 | <mills@udel.edu></a></address> |
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| 259 | </body> |
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| 260 | </html> |
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| 261 | |
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