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<title>NTP Version 4 Release Notes</title>
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<h3>NTP Version 4 Release Notes</h3>
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<img align="left" src="pic/hornraba.gif" alt="gif"><a href=
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"http://www.eecis.udel.edu/~mills/pictures.htm">from <i>Alice's
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Adventures in Wonderland</i>, Lewis Carroll</a>
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<p>The rabbit toots to make sure you read this.<br clear="left">
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<p>This document was last updated 4 May 2001</p>
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<h4>NTP Version 4 Release Notes</h4>
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<p>This release of the NTP Version 4 (NTPv4) daemon for Unix, VMS
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and Windows (NT4 and 2000) incorporates new features and
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refinements to the NTP Version 3 (NTPv3) algorithms. However, it
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continues the tradition of retaining backwards compatibility with
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older versions, except for symmetric mode in NTPv1. Client/server
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mode continues to be supported in NTPv1. The NTPv4 version has been
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under development for quite a while and isn't finished yet. In
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fact, quite a number of NTPv4 features have already been
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retrofitted in the current NTPv3, although this version is not
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actively maintained by the NTPv4 developer's group.</p>
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<p>The primary purpose of this release is to verify the remaining
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new code compiles and runs in the various architectures, operating
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systems and hardware complement that can't be verified here. Of
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particular interest are Windows 2000, VMS and various reference
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clock drivers. As always, corrections and bugfixes are warmly
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received, especially in the form of context diffs.</p>
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<p>This note summarizes the differences between this software
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release of NTPv4, called ntp-4.x.x, and the previous NTPv3 version,
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called xntp3-5.x.x. Additional information on protocol
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compatibility details is in the <a href="biblio.htm">Protocol
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Conformance Statement</a> page.</p>
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<p>Most calculations are now done using 64-bit floating double
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format, rather than 64-bit fixed point format. The motivation for
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this is to reduce size, improve speed and avoid messy bounds
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checking. Workstations of today are much faster than when the
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original NTP version was designed in the early 1980s, and it is
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rare to find a processor architecture that does not support
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floating double. The fixed point format is still used with raw
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timestamps, in order to retain the full precision of about 212
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picoseconds. However, the algorithms which process raw timestamps
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all produce fixed point differences before converting to floating
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double. The differences are ordinarily quite small so can be
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expressed without loss of accuracy in this format.</p>
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<p>The clock discipline algorithm has been redesigned to improve
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accuracy, reduce the impact of network jitter and allow an increase
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in poll intervals to well over one day with only moderate sacrifice
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in accuracy. The NTPv4 design allows servers to increase the poll
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intervals even when synchronized directly to the peer. In NTPv3 the
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poll interval in such cases was clamped to the minimum, usually 64
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s. For those servers with hundreds of clients, the new design can
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dramatically reduce the network load.</p>
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<p>This release includes support for the <a href=
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"http://www.eecis.udel.edu/~mills/resource.htm"><i>
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nanokernel</i></a> precision time kernel support, which is now in
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stock Linux and FreeBSD kernels. If a precision time source such as
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a GPS timing receiver or cesium clock is available, kernel
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timekeeping can be improved to the order less than one microsecond.
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The older precision time kernel for the Alpha continues to be
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<p>This release includes support for Autokey public-key
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cryptography, which is the preferred scheme for authenticating
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servers to clients. It uses NTP header extensions fields documented
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in: Mills, D.L. Public-Key cryptography for the Network Time
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Protocol. Internet Draft draft-ietf-stime-ntpauth-00.txt,
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University of Delaware, June 2000, 36 pp. <a href=
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"http://www.eecis.udel.edu/~mills/database/memos/draft-ietf-stime-ntpauth-00.txt">
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ASCII</a> and implemented in this release. The design provides for
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orderly key refreshment and does not require public keys and
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related media to be copied from one machine to another. Specific
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information about Autokey cryptography is contained in the <a href=
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"authopt.htm">Authentication Options</a> page and links from
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<p>NTPv4 includes two new association modes which in most
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applications can avoid per-host configuration altogether. Both of
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these are based on IP multicast technology and Autokey
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cryptography. They provide for automatic discovery and
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configuration of servers and clients without identifying servers or
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clients in advance. In multicast mode a server sends a message at
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fixed intervals using specified multicast group addresses, while
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clients listen on these addresses. Upon receiving the message, a
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client exchanges several messages with the server in order to
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calibrate the multicast propagation delay between the client and
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server. In manycast mode a client sends a message to a specified
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multicast group address and expects one or more servers to reply.
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Using engineered algorithms, the client selects an appropriate
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subset of servers from the messages received and continues in
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ordinary client/server operation. The manycast scheme can provide
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somewhat better accuracy than the multicast scheme at the price of
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additional network overhead. See the <a href="assoc.htm">
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Association Management</a> page for further information.</p>
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<p>There are two burst mode features available where special
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conditions apply. One of these is enabled by the <tt>iburst</tt>
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keyword in the <tt>server</tt> configuration command. It is
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intended for cases where it is important to set the clock quickly
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when an association is first mobilized. The other is enabled by the
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<tt>burst</tt> keyword in the <tt>server</tt> configuration
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command. It is intended for cases where the network attachment
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requires an initial calling or training procedure. See the <a href=
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"assoc.htm">Association Management</a> page for further
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<p>The reference clock driver interface is smaller, more rational
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and more accurate. Support for pulse-per-second (PPS) signals has
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been extended to all drivers as an intrinsic function. Most of the
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drivers in NTPv3 have been converted to this interface, but some,
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including the PARSE subinterface, have yet to be overhauled. New
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drivers have been added for several GPS receivers now on the market
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for a total of 39 drivers. Drivers for the Canadian standard time
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and frequency station CHU, the US standard time and frequency
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stations WWV/H and for IRIG signals have been updated and
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capabilities added to allow direct connection of these signals to
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the Sun audio port <tt>/dev/audio</tt>.</p>
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<p>In all except a very few cases, all timing intervals are
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randomized, so that the tendency for NTPv3 to self-synchronize and
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bunch messages, especially with a large number of configured
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associations, is minimized.</p>
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<p>In NTPv3 a large number of weeds and useless code had grown over
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the years since the original NTPv1 code was implemented almost
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twenty years ago. Using a powerful weedwacker, much of the
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shrubbery has been removed, with effect a substantial reduction in
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size of almost 40 percent.</p>
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<p>The entire distribution has been converted to gnu <tt>
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automake</tt>, which should greatly ease the task of porting to new
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and different programming environments, as well as reduce the
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incidence of bugs due to improper handling of idiosyncratic kernel
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<h4>Nasty Surprises</h4>
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<p>There are a few things different about this release that have
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changed since the latest NTP Version 3 release. Following are a few
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things to worry about:</p>
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<p>As required by Defense Trade Regulations (DTR), the
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cryptographic routines supporting the Data Encryption Standard
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(DES) have been removed from the base distribution. These routines
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are readily available in most countries from RSA Laboratories.
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Directions for their use are in the <a href="build.htm">Building
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and Installing the Distribution</a> page.</p>
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<p>As the result of the above, the <tt>./authstuff</tt> directory,
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intended as a development and testing aid for porting cryptographic
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routines to exotic architectures, has been removed. Developers
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should note the NTP authentication routines use the interface
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defined in the <tt>rsaref2.0</tt> package available from RSA
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<p>The enable and disable commands have a few changes in their
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arguments see the <tt>ntpd</tt> <a href="confopt.htm">Configuration
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Options</a> page for details. Note that the <tt>authenticate</tt>
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command has been removed.</p>
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<p>The <tt>ppsclock</tt> line discipline/streams module is no
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longer supported. This function is now handled by the <a href=
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"driver22.htm">PPS Clock Discipline</a> driver, which uses the new
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PPSAPI application program interface proposed by the IETF. Note
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that the <tt>pps</tt> configuration file command has been obsoleted
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by the driver. See the <a href="pps.htm">Pulse-per-second (PPS)
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Signal Interfacing</a> page for further information.</p>
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<p>Several new options have been added for the <tt>ntpd</tt>
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command line. For the inveterate knob twiddlers several of the more
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important performance variables can be changed to fit actual or
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perceived special conditions. It is possible to operate the daemon
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in a one-time mode similar to <tt>ntpdate</tt>, which program is
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headed for retirement. See the <a href="ntpd.htm"><tt>ntpd</tt> -
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Network Time Protocol (NTP) daemon</a> page for the new
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<p>To help reduce the level of spurious network traffic due to
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obsolete configuration files, a special control message called the
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kiss-of-death packet has been implemented. If enabled and a packet
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is denied service or exceeds the client limie, a compliant server
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will send this message to the client. A compliant client will cease
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further transmission and send a message to the system log. See the
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<a href="accopt.htm">Authentication Options</a> page for further
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<p>An experimental filter algorithm called huff-n'-puff has been
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implemented to reduce errors under conditions of severe assymetric
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delays characteristic of <tt>ppp</tt> connections with telephone
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modems and downloading or uploading considerable traffic. See the
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<a href="ntpd.htm">ntpd - Network Time Protocol (NTP) daemon</a>
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page for further information.</p>
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<p>This release has been compiled and tested on several systems,
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including SunOS 4.1.3, Solaris 2.5.1-2.8, Alpha 4.0, Ultrix 4.4,
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Linux, FreeBSD and HP-UX 10.02. It has been compiled and tested on
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Windows NT, but not yet on any other Windows version or for VMS. We
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are relying on the NTP volunteer corps to do that. Known problems
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are summarized below:</p>
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<p>The latest NTPv4 <tt>ntpdc</tt> does not work with previous
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versions of <tt>ntpd</tt> and previous versions of <tt>ntpdc</tt>
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do not work with latest <tt>ntpd</tt>. This situation is
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regrettable and may be fixed in future; however, it is necessary in
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order for the autokey function to retrieve canonical names and
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certificates from directory services such as Secure DNS.</p>
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<p>The precision time support in stock Solaris 2.6 has bugs that
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were fixed in 2.7. A patch is available that fixes the 2.6 bugs.
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The 2.6 kernel discipline has been disabled by default. For
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testing, the kernel can be enabled using the <tt>enable kernel</tt>
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command either in the configuration file or via <tt>ntpdc</tt>.</p>
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<p>The HTML documentation has been partially updated. However, most
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of the NTPv3 documentation continues to apply to NTPv4. Until the
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update happens, what you see is what you get. We are always happy
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to accept comments, corrections and bug reports. However, we are
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most thrilled upon receipt of patches to fix the dang bugs.</p>
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<a href="index.htm"><img align="left" src="pic/home.gif" alt=
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<address><a href="mailto:mills@udel.edu">David L. Mills
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<mills@udel.edu></a></address>
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