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diff --git a/html/index.html b/html/index.html index 5c19313176e3..9ba5c6fcac20 100644 --- a/html/index.html +++ b/html/index.html @@ -13,84 +13,75 @@ <h3>The Network Time Protocol (NTP) Distribution</h3> <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> <p>Pleased to meet you.</p> - <p>Last update: <csobj format="ShortTime" h="25" locale="00000409" region="0" t="DateTime" w="61">18:39</csobj> UTC <csobj format="LongDate" h="25" locale="00000409" region="0" t="DateTime" w="246">Thursday, July 28, 2005</csobj></p> - <br clear="left"> + <p>Last update: + <!-- #BeginDate format:En2m -->07-Nov-2009 20:43<!-- #EndDate --> + UTC</p> +<br clear="left"> <h4>Related Links</h4> - <script type="text/javascript" language="javascript" src="scripts/links7.txt"></script> - <br clear="left"> - <h4>Table of Contents</h4> <ul> - <li class="inline"><a href="#intro">Introduction</a> - <li class="inline"><a href="#build">Building and Installing NTP</a> - <li class="inline"><a href="#conf">Configuring Clients and Servers</a> - <li class="inline"><a href="#prog">Program Manual Pages</a> - <li class="inline"><a href="#docs">Supporting Documentation</a> - <li class="inline"><a href="#back">Background Information</a> - <li class="inline"><a href="#app">Application Notes</a> + <li>A list of all links is on the <a href="sitemap.html">Site Map</a> page.</li> </ul> + <h4>Table of Contents</h4> + <ul> + <li class="inline"><a href="#intro">Introduction</a></li> + <li class="inline"><a href="#build">Building and Installing NTP</a></li> + <li class="inline"><a href="#conf">Configuring Clients and Servers</a></li> + <li class="inline"><a href="#opt">Features and Options</a></li> + <li class="inline"><a href="#prob">Resolving Problems</a></li> + <li class="inline"><a href="#info">Further Information</a></li> + </ul> <hr> <h4 id="intro">Introduction</h4> - <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> - <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> - <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> - <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> + <p>Note: The NTP Version 4 software contained in this distribution is available without charge under the conditions set forth in the <a href="copyright.html">Copyright Notice</a>.</p> + <dl> + <dd>It is very important that readers understand that the NTP document collection began 25 years ago and remains today a work in progress. It has evolved as new features were invented and old features retired. It has been widely copied, cached and morphed to other formats, including man pages, with varying loss of fidelity. However, these HTML pages are the ONLY authoritative and definitive reference. Readers should always use the collection that comes with the distribution they use. A copy of the online collection at <a href="http://www.ntp.org">www.ntp.org</a> is normally included in the most recent snapshot, but might not agree with an earlier snapshot or release version.</dd> + </dl> + <p>The Network Time Protocol (NTP) is widely used to synchronize a computer + to Internet time servers or other sources, such as a radio or satellite + receiver or telephone modem service. It can also be used as a server + for dependent clients. It provides accuracies typically less than + a millisecond on LANs and up to a few milliseconds on WANs. Typical + NTP configurations utilize multiple redundant servers and diverse + network paths in order to achieve high accuracy and reliability. + Authentication is provided using symmetric key cryptography and + the MD5 message digest algorithm included in the distribution. If + the OpenSSL cryptographic library is installed, the SHA or SHA1 message + digest algorithms can be used. If the OpenSSL library is installed, + additional options based on public key cryptography are available.</p> + <p>NTP time synchronization services are widely available in the public Internet. + The public NTP subnet in early 2008 includes several thousand servers + in most countries and on every continent of the globe, including Antarctica. + These servers support a total population estimated at over 25 million computers + in the global Internet. The NTP subnet operates with a hierarchy of levels, + where each level is assigned a number called the stratum. Stratum 1 (primary) + servers at the lowest level are directly synchronized to national time services. + Stratum 2 (secondary) servers at the next higher level are synchronize to stratum + 1 servers and so on. Normally, NTP clients and servers with a relatively small + number of clients do not synchronize to public primary servers. There + are several hundred public secondary servers operating at higher strata and + are the preferred choice. </p> + <p>Background information on computer network time synchronization is on the <a href="http://www.eecis.udel.edu/%7emills/exec.html">Executive Summary - Computer Network Time Synchronization</a> page. Discussion on new features and interoperability with previous NTP versions is on the <a href="release.html">NTP Version 4 Release Notes</a> page. Background information, bibliography and briefing slides suitable for presentations are on the <a href="http://www.eecis.udel.edu/%7emills/ntp.html">Network Time Synchronization Research Project</a> page. Additional information is at the NTP web site <a href="http://www.ntp.org">www.ntp.org</a>.</p> <h4 id="build">Building and Installing NTP</h4> - <p>NTP supports Unix and Windows (XP, NT4 and 2000) systems. The <a href="build/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="build/config.html">Configuration Options</a> and <a href="release.html">Release Notes</a> pages.</p> - <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> - <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> - <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> + <p>NTP supports Unix, VMS and Windows (Vista, XP, NT4 and 2000) systems. The <a href="build.html">Building and Installing the Distribution</a> page details the procedures for building and installing on a typical system. This distribution includes drivers for 44 radio and satellite receivers and telephone modem services in the US, Canada and Europe. A list of supported drivers is on the <a href="refclock.html">Reference Clock Drivers</a> page. The default build includes the debugging options and all drivers that run on the target machine; however, options and drivers can be included or excluded using options on the <a href="config.html">Configuration Options</a> page.</p> <h4 id="conf">Configuring Clients and Servers</h4> - <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="build/quick.html">Quick Start</a> page may be useful to get a simple workstation on the air with an existing server.</p> - <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> - <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> - <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> - <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> + <p>NTP is by its very nature a complex distributed network application and can be configured for widely divergent timekeeping scenarios. The documentation on these pages attempts to cover the entire suite of configuration, operation and maintenance features which this distribution supports. However, most applications will need only a few of these features. The <a href="quick.html">Quick Start</a> page may be useful to get a simple workstation on the air with existing servers.</p> + <p>The most important factor in providing accurate, reliable time is the selection of modes and servers in the configuration file. A discussion on the available modes is on the <a href="assoc.html">Association Management</a> page. The current public server list is maintained at the <a href="http://www.ntp.org">www.ntp.org</a> web site. In many cases the configuration can be automated using the schemes described on the <a href="manyopt.html">Automatic Server Discovery Schemes</a> page.</p> + <h4 id="opt">Features and Options</h4> + <p>This distribution includes a statistics data recording facility which can record performance statistics and events of various types for retrospective analysis. These include time and frequency statistics, significant events and usage statistics described on the <a href="monopt.html">Monitoring Options</a> page.</p> + <p>Some programs included in this distribution use cryptographic algorithms to verify server authenticity. Where local security policy permits relatively weak symmetric key cryptography, the required software is included in this distribution. Where local policy requires stronger public key cryptography, the OpenSSL library available from <a href="http://www.openssl.org">http://www.openssl.org</a> is required. This library is also used by the Secure Shell facility, so is often already installed. Additional details are on the <a href="authopt.html">Authentication Options</a> page.</p> + <p>This distribution includes features that can restrict access in various ways as described on the <a href="accopt.html">Access Control Options</a> page. This can be used to deny service if not authenticated, deny service requiring persistent resources or deny service altogether.</p> + <p>This distribution includes a simulation framework in which substantially + all the runtime NTP operations and most features can be tested and + evaluated. This has been very useful in exploring in vitro response + to unusual circumstances or over time periods impractical in vivo. Details + are on the <a href="ntpdsim.html">Network + Time Protocol (NTP) Simulator</a> page.</p> <h4 id="prob">Resolving Problems</h4> - <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="build/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> - <p>Users are requested to report bugs, offer suggestions and contribute additions to this distribution. The <a href="build/patches.html">Patching Procedures</a> page suggests procedures which greatly simplify distribution updates, while the <a href="build/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> - <h4 id="prog">Program Manual Pages</h4> - <ul> - <li class="inline"><a href="ntpd.html"><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a> - <li class="inline"><a href="ntpq.html"><tt>ntpq</tt> - standard NTP query program</a> - <li class="inline"><a href="ntpdc.html"><tt>ntpdc</tt> - special NTP query program</a> - <li class="inline"><a href="ntpdate.html"><tt>ntpdate</tt> - set the date and time via NTP</a> - <li class="inline"><a href="ntptrace.html"><tt>ntptrace</tt> - trace a chain of NTP servers back to the primary source</a> - <li class="inline"><a href="tickadj.html"><tt>tickadj</tt> - set time-related kernel variables</a> - <li class="inline"><a href="ntptime.html"><tt>ntptime</tt> - read kernel time variables</a> - <li class="inline"><a href="keygen.html"><tt>ntp-keygen</tt> - generate public and private keys</a> - <li class="inline"><a href="ntpdsim.html"><tt>ntpdsim</tt> - Network Time Protocol (NTP) simulator</a> - </ul> - <h4 id="docs">Supporting Documentation</h4> - <ul> - <li class="inline"><a href="copyright.html">Copyright Notice</a> - <li class="inline"><a href="notes.html">Notes on Configuring NTP and Setting up a NTP Subnet</a> - <li class="inline"><a href="release.html">NTP Version 4 Release Notes</a> - <li class="inline"><a href="build/build.html">Building and Installing the Distribution</a> - <li class="inline"><a href="build/config.html">Configuration Options</a> - <li class="inline"><a href="refclock.html">Reference Clock Drivers</a> - <li class="inline"><a href="debug.html">NTP Debugging Techniques</a> - <li class="inline"><a href="rdebug.html">Debugging Reference Clock Drivers</a> - <li class="inline"><a href="msyslog.html"><tt>ntpd</tt> System Log Messages</a> - <li class="inline"><a href="build/patches.html">Patching Procedures</a> - <li class="inline"><a href="build/hints.html">Hints and Kinks</a> - <li class="inline"><a href="build/porting.html">Porting Hints</a> - </ul> - <h4 id="back">Background Information</h4> - <ul> - <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/ntp.html">NTP Project and Reference Library</a> - <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/exec.html">Executive Summary - Computer Network Time Synchronization</a> - <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/y2k.html">The Network Time Protocol Timescale and Era Numbering</a> - <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/leap.html">NTP Timescale and Leap Seconds</a> - <li class="inline"><a href="http://www.eecis.udel.edu/%7emills/biblio.html">Protocol Conformance Statement</a> - </ul> - <h4 id="app">Application Notes</h4> - <ul> - <li class="inline"><a href="prefer.html">Mitigation Rules and the <tt>prefer</tt> Keyword</a> - <li class="inline"><a href="assoc.html">Association Management</a> - <li class="inline"><a href="pps.html">Pulse-per-second (PPS) Signal Interfacing</a> - <li class="inline"><a href="measure.html">Time and Time Interval Measurement with Application to Computer and Network Performance Evaluation</a> - <li class="inline"><a href="kern.html">Kernel Model for Precision Timekeeping</a> - </ul> + <p>Like other things in modern Internet life, NTP problems can be devilishly intricate. This distribution includes a number of utilities designed to identify and repair problems using an integrated management protocol supported by the <a href="ntpq.html"><tt>ntpq</tt></a> utility program In addition, the <a href="ntpdc.html"><tt>ntpdc</tt></a> utility program can be useful in some cases.</p> + <p>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. Additional information on reference clock driver construction and debugging is in the <a href="rdebug.html">Debugging Hints for Reference Clock Drivers</a> page.</p> + <p>Users are invited to report bugs and offer suggestions via the <a href="bugs.html">NTP Bug Reporting Procedures</a> page.</p> + <h4 id="info">Further Information</h4> + <p>The <a href="sitemap.html">Site Map</a> page contains a list of document collections arranged by topic. The Program Manual Pages collection may be the best place to start, followed by the <a href="comdex.html"></a>Configuration Commands and Options collection. The <a href="comdex.html">Command Index</a> collection contains a list of all configuration file commands together with a short function description. A great wealth of additional information is available via the External Links collection, including a book and numerous background papers and briefing presentations.</p> <hr> <div align="center"> <img src="pic/pogo1a.gif" alt="gif"></div> |