19c2daa00SOllivier Robert<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 29c2daa00SOllivier Robert 39c2daa00SOllivier Robert<html> 49c2daa00SOllivier Robert 59c2daa00SOllivier Robert <head> 69c2daa00SOllivier Robert <meta name="generator" content="HTML Tidy, see www.w3.org"> 79c2daa00SOllivier Robert <title>The Network Time Protocol (NTP) Distribution</title> 89c2daa00SOllivier Robert <link href="scripts/style.css" type="text/css" rel="stylesheet"> 99c2daa00SOllivier Robert </head> 109c2daa00SOllivier Robert 119c2daa00SOllivier Robert <body> 129c2daa00SOllivier Robert <h3>The Network Time Protocol (NTP) Distribution</h3> 139c2daa00SOllivier Robert <img src="pic/barnstable.gif" alt="gif" align="left"><a href="http://www.eecis.udel.edu/%7emills/pictures.html"><i>P.T. Bridgeport Bear</i>; from <i>Pogo</i>, Walt Kelly</a> 149c2daa00SOllivier Robert <p>Pleased to meet you.</p> 159c2daa00SOllivier Robert <p>Last update: <csobj format="ShortTime" h="25" locale="00000409" region="0" t="DateTime" w="99">03:12 AM</csobj> UTC <csobj format="LongDate" h="25" locale="00000409" region="0" t="DateTime" w="270">Monday, October 13, 2003</csobj></p> 169c2daa00SOllivier Robert <br clear="left"> 179c2daa00SOllivier Robert <h4>Related Links</h4> 189c2daa00SOllivier Robert <script type="text/javascript" language="javascript" src="scripts/links7.txt"></script> 199c2daa00SOllivier Robert <br clear="left"> 209c2daa00SOllivier Robert <h4>Table of Contents</h4> 219c2daa00SOllivier Robert <ul> 229c2daa00SOllivier Robert <li class="inline"><a href="#intro">Introduction</a> 239c2daa00SOllivier Robert <li class="inline"><a href="#build">Building and Installing NTP</a> 249c2daa00SOllivier Robert <li class="inline"><a href="#conf">Configuring Clients and Servers</a> 259c2daa00SOllivier Robert <li class="inline"><a href="#conf">Configuring Clients and Servers</a> 269c2daa00SOllivier Robert <li class="inline"><a href="#prog">Program Manual Pages</a> 279c2daa00SOllivier Robert <li class="inline"><a href="#docs">Supporting Documentation</a> 289c2daa00SOllivier Robert <li class="inline"><a href="#back">Background Information</a> 299c2daa00SOllivier Robert <li class="inline"><a href="#app">Application Notes</a> 309c2daa00SOllivier Robert </ul> 319c2daa00SOllivier Robert <hr> 329c2daa00SOllivier Robert <h4 id="intro">Introduction</h4> 339c2daa00SOllivier Robert <p>Note: The software contained in this distribution is available without charge under the conditions set forth in the <a href="copyright.html">Copyright Notice</a>.</p> 349c2daa00SOllivier Robert <p>The Network Time Protocol (NTP) is used to synchronize the time of a computer client or server to another server or reference time source, such as a radio or satellite receiver or modem. It provides accuracies typically within a millisecond on LANs and up to a few tens of milliseconds on WANs relative to Coordinated Universal Time (UTC) via a Global Positioning Service (GPS) receiver, for example. Typical NTP configurations utilize multiple redundant servers and diverse network paths in order to achieve high accuracy and reliability.</p> 359c2daa00SOllivier Robert <p>This software release implements NTP Version 4 (NTPv4), but is in general backwards compatible with previous versions except NTP Version 1, support for which is no longer viable. NTPv4 includes support for both symmetric key and public key cryptography to prevent accidental or malicious protocol attacks, as well as automatic server discovery using IP multicast means. This release includes full support for the IPv6 address family, where the operating system supports it, as well as the default IPv4 address family. Either or both families can be used at the same time on the same machine.</p> 369c2daa00SOllivier Robert <p>Background information on computer network time synchronization can be found on the <a href="http://www.eecis.udel.edu/%7emills/exec.html">Executive Summary - Computer Network Time Synchronization</a> page. Discussion on protocol conformance issues and interoperability with previous NTP versions can be found on the <a href="http://www.eecis.udel.edu/%7emills/biblio.html">Protocol Conformance Statement</a> page. Discussion on how NTP reckons the time can be found on the <a href="http://www.eecis.udel.edu/%7emills/leap.html">NTP Timescale and Leap Seconds</a> page. Background information, bibliography and briefing slides suitable for presentations can be found on the <a href="http://www.eecis.udel.edu/%7emills/ntp.html">Network Time Synchronization Project</a> page. Additional information can be found at the NTP web site <a href="http://www.ntp.org">www.ntp.org</a>. Please send bug reports to <a href="mailto:bugs@mail.ntp.org"><bugs@mail.ntp.org></a>.</p> 379c2daa00SOllivier Robert <h4 id="build">Building and Installing NTP</h4> 389c2daa00SOllivier Robert <p>NTP supports Unix and Windows (NT4 and 2000) systems. The <a href="build.html">Building and Installing the Distribution</a> page presents an overview of the procedures for compiling the distribution and installing it on a typical client or server. The build procedures inspect the system hardware and software environment and automatically select the appropriate options for that environment. While these procedures work with most computers and operating systems marketed today, exceptions requiring manual intervention do exist, as documented on the <a href="config.html">Configuration Options</a> and <a href="release.html">Release Notes</a> pages.</p> 399c2daa00SOllivier Robert <p>Bringing up a NTP primary server requires a radio or satellite receiver or modem. The distribution includes hardware drivers for some forty radio and satellite clocks and modem services. A list of supported drivers is given on the <a href="refclock.html">Reference Clock Drivers</a> page. It is also possible to use an otherwise undisciplined machine as a primary or backup server, as described on the <a href="drivers/driver1.html">Undisciplined Local Clock</a> page. For most popular workstations marketed by Sun, Silicon Graphics and Hewlett Packard, as well as widely available Unix clones such as FreeBSD and Linux, the automatic build procedures select all drivers that run on the target machine. While this increases the size of the executable binary somewhat, individual drivers can be included or excluded using the configure utility documented in the Configuration Options page.</p> 409c2daa00SOllivier Robert <p>Some programs included in this distribution use cryptographic algorithms to verify authenticity and credentials. Where local security policy permits relatively weak symmetric key cryptography, the required software is included in this distribution. However, where local policy requires stronger public key cryptography, additional software not in this distribution is required. This distribution uses the OpenSSL library available from <a href="http://www.openssl.org">http://www.openssl.org</a>. This library is also used by the Secure Shell facility, so is often already installed on Unix workstations and servers. It includes support for most message digest and digital signature algorithms used in the industry, as well as X.509 certificate generation, signing and verification.</p> 419c2daa00SOllivier Robert <p>While public key cryptography is optional but highly recommended for all NTP operations, it is required for the NTPv4 Autokey protocol described on the <a href="http://www.eecis.udel.edu/%7emills/autokey.html">Autonomous Authentication</a> page and is an integral component of the generic automatic configuration scheme described on the <a href="http://www.eecis.udel.edu/%7emills/autocfg.html">Autonomous Configuration</a> page. In addition, access can be restricted in various ways described on the <a href="accopt.html">Access Control Options</a> page.</p> 429c2daa00SOllivier Robert <h4 id="conf">Configuring Clients and Servers</h4> 439c2daa00SOllivier Robert <p>NTP is by its very nature a complex distributed network application and can be configured and used for a great many widely divergent timekeeping scenarios. The documentation presented on these pages attempts to cover the entire suite of configuration, operation and maintenance facilities which this distribution supports. However, most applications will need only a few of these facilities. If this is the case, the <a href="quick.html">Quick Start</a> page may be useful to get a simple workstation on the air with an existing server.</p> 449c2daa00SOllivier Robert <p>However, in order to participate in the existing NTP synchronization subnet and obtain accurate, reliable time, it is usually necessary to construct an appropriate configuration file, commonly called <tt>ntp.conf</tt>, which establishes the servers and/or external receivers or modems to be used by this particular machine. Directions for constructing this file are in the <a href="notes.html">Notes on Configuring NTP and Setting up a NTP Subnet</a> page. However, in many common cases involving simple network topologies and workstations, the configuration data can be specified entirely on the command line for the <a href="ntpd.html"><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a>.</p> 459c2daa00SOllivier Robert <p>The most important factor in providing accurate, reliable time is the selection of modes and servers to be used in the configuration file. A discussion on the available modes is on the <a href="assoc.html">Association Management</a> page. NTP support for one or more computers is normally engineered as part of the existing public NTP synchronization subnet. The public subnet consists of a multiply redundant hierarchy of servers and clients, with each level in the hierarchy identified by stratum number. Primary servers operate at stratum one and provide synchronization to secondary servers operating at stratum two and so on to higher strata. In this hierarchy, clients are simply servers that have no dependents.</p> 469c2daa00SOllivier Robert <p>Configuring a corporate or campus NTP subnet can be an engineering challenge. NTP contains many features designed to survive system and network failures, software bugs, clock errors and hacker attacks. Surviving these hazards requires intricate design of the timekeeping network using good principles of server redundancy and path diversity. The Manycast mode, new to NTPv4, is designed to track the current server and network states and adjust the client/server configuration for the best available accuracy and reliability. More information on the Manycast mode is on the <a href="authopt.html">Athentication Options</a> and <a href="manyopt.html">Automatic NTP Configuration Options</a> pages.</p> 479c2daa00SOllivier Robert <p>The NTP subnet in early 2003 includes well over a hundred public primary (stratum 1) servers synchronized directly to UTC by radio, satellite or modem and located in every continent of the globe, including Antarctica. Normally, client workstations and servers with a relatively small number of clients do not synchronize to primary servers. There are well over a hundred public secondary (stratum 2) servers synchronized to the primary servers and providing synchronization to a total well over 100,000 clients and servers in the Internet. The current lists are maintained on the <a href="http://www.eecis.udel.edu/%7emills/ntp/index.html">Information on Time and Frequency Services</a> page, which is updated frequently. There are thousands upon thousands of private primary and secondary servers not normally available to the public, many hiding behind firewalls. Clients are strongly discouraged against using these servers, since they sometimes hide in little ghettos behind dinky links to the outside world and unwanted traffic can bring up expensive ISDN lines, causing much grief and frustration. There are defensive means described on the Access Control Options page, including the Kiss-of-Death packet.</p> 489c2daa00SOllivier Robert <h4 id="prob">Resolving Problems</h4> 499c2daa00SOllivier Robert <p>Like other things Internet, the NTP synchronization subnets tend to be large and devilishly intricate, with many opportunities for misconfiguration and network problems. The NTP engineering model is specifically designed to help isolate and repair such problems using an integrated management protocol, together with a suite of monitoring and debugging tools. There is an optional statistics data recording facility which can be used to record normal and aberrant operation, log problems to the system log facility, and retain records of client access. The <a href="debug.html">NTP Debugging Techniques</a> and <a href="hints.html">Hints and Kinks</a> pages contain useful information for identifying problems and devising solutions. In extreme cases, problems can be detected through the use of the <a href="ntpdsim.html"><tt>ntpdsim</tt> - Network Time Protocol (NTP) simulator</a> included in this software distribution.</p> 509c2daa00SOllivier Robert <p>Users are requested to report bugs, offer suggestions and contribute additions to this distribution. The <a href="patches.html">Patching Procedures</a> page suggests procedures which greatly simplify distribution updates, while the <a href="porting.html">Porting Hints</a> page suggest ways to make porting this code to new hardware and operating systems easier. Additional information on reference clock driver construction and debugging can be found in the <a href="rdebug.html">Debugging Hints for Reference Clock Drivers</a> page.</p> 519c2daa00SOllivier Robert <h4 id="prog">Program Manual Pages</h4> 529c2daa00SOllivier Robert <ul> 539c2daa00SOllivier Robert <li class="inline"><a href="ntpd.html"><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a> 549c2daa00SOllivier Robert <li class="inline"><a href="ntpq.html"><tt>ntpq</tt> - standard NTP query program</a> 559c2daa00SOllivier Robert <li class="inline"><a href="ntpdc.html"><tt>ntpdc</tt> - special NTP query program</a> 569c2daa00SOllivier Robert <li class="inline"><a href="ntpdate.html"><tt>ntpdate</tt> - set the date and time via NTP</a> 579c2daa00SOllivier Robert <li class="inline"><a href="ntptrace.html"><tt>ntptrace</tt> - trace a chain of NTP servers back to the primary source</a> 589c2daa00SOllivier Robert <li class="inline"><a href="tickadj.html"><tt>tickadj</tt> - set time-related kernel variables</a> 599c2daa00SOllivier Robert <li class="inline"><a href="ntptime.html"><tt>ntptime</tt> - read kernel time variables</a> 609c2daa00SOllivier Robert <li class="inline"><a href="keygen.html"><tt>ntp-genkeys</tt> - generate public and private keys</a> 619c2daa00SOllivier Robert <li class="inline"><a href="ntpdsim.html"><tt>ntpdsim</tt> - Network Time Protocol (NTP) simulator</a> 629c2daa00SOllivier Robert </ul> 639c2daa00SOllivier Robert <h4 id="docs">Supporting Documentation</h4> 649c2daa00SOllivier Robert <ul> 659c2daa00SOllivier Robert <li class="inline"><a href="copyright.html">Copyright Notice</a> 669c2daa00SOllivier Robert <li class="inline"><a href="notes.html">Notes on Configuring NTP and Setting up a NTP Subnet</a> 679c2daa00SOllivier Robert <li class="inline"><a href="release.html">NTP Version 4 Release Notes</a> 689c2daa00SOllivier Robert <li class="inline"><a href="build.html">Building and Installing the Distribution</a> 699c2daa00SOllivier Robert <li class="inline"><a href="config.html">Configuration Options</a> 709c2daa00SOllivier Robert <li class="inline"><a href="refclock.html">Reference Clock Drivers</a> 719c2daa00SOllivier Robert <li class="inline"><a href="debug.html">NTP Debugging Techniques</a> 729c2daa00SOllivier Robert <li class="inline"><a href="rdebug.html">Debugging Reference Clock Drivers</a> 739c2daa00SOllivier Robert <li class="inline"><a href="msyslog.html"><tt>ntpd</tt> System Log Messages</a> 749c2daa00SOllivier Robert <li class="inline"><a href="patches.html">Patching Procedures</a> 759c2daa00SOllivier Robert <li class="inline"><a href="hints.html">Hints and Kinks</a> 769c2daa00SOllivier Robert <li class="inline"><a href="porting.html">Porting Hints</a> 779c2daa00SOllivier Robert </ul> 789c2daa00SOllivier Robert <h4 id="back">Background Information</h4> 799c2daa00SOllivier Robert <ul> 809c2daa00SOllivier Robert <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/ntp.html">NTP Project and Reference Library</a> 819c2daa00SOllivier Robert <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/exec.html">Executive Summary - Computer Network Time Synchronization</a> 829c2daa00SOllivier Robert <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/y2k.html">The Network Time Protocol Timescale and Era Numbering</a> 839c2daa00SOllivier Robert <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/leap.html">NTP Timescale and Leap Seconds</a> 849c2daa00SOllivier Robert <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/biblio.html">Protocol Conformance Statement</a> 859c2daa00SOllivier Robert </ul> 869c2daa00SOllivier Robert <h4 id="app">Application Notes</h4> 879c2daa00SOllivier Robert <ul> 889c2daa00SOllivier Robert <li class="inline"><a href="prefer.html">Mitigation Rules and the <tt>prefer</tt> Keyword</a> 899c2daa00SOllivier Robert <li class="inline"><a href="assoc.html">Association Management</a> 909c2daa00SOllivier Robert <li class="inline"><a href="pps.html">Pulse-per-second (PPS) Signal Interfacing</a> 919c2daa00SOllivier Robert <li class="inline"><a href="measure.html">Time and Time Interval Measurement with Application to Computer and Network Performance Evaluation</a> 929c2daa00SOllivier Robert <li class="inline"><a href="kern.html">Kernel Model for Precision Timekeeping</a> 939c2daa00SOllivier Robert </ul> 949c2daa00SOllivier Robert <hr> 959c2daa00SOllivier Robert <div align="center"> 969c2daa00SOllivier Robert <img src="pic/pogo1a.gif" alt="gif"></div> 979c2daa00SOllivier Robert <br> 989c2daa00SOllivier Robert <script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 999c2daa00SOllivier Robert </body> 1009c2daa00SOllivier Robert 1019c2daa00SOllivier Robert</html>
