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6 <title>NTP Version 4 Release Notes</title>
10 <h3>NTP Version 4 Release Notes</h3>
14 <!-- #BeginDate format:En1m -->3-Oct-2011 21:51<!-- #EndDate -->
22 <li class="inline"><a href="#change">Changes and Upgrades Since the NTPv3 Version (xntp3-5)</a></li>
26 <p>NTP has been under development for almost 30 years, but the paint ain't dry even now. This release of the NTP Version 4 (NTPv4) distribution for Unix, VMS and Windows incorporates new features and refinements, but retaining backwards compatibility with older versions, including NTPv3 and NTPv2, but not NTPv1. Support for NTPv1 has been discontinued because of certain security vulnerabilities.</p>
34 <li>The huff-n'-puff filter is designed to avoid large errors with DSL circuits and highly asymmetrical traffic, as when downloading large files. Details are on the <a href="huffpuff.html">The Huff-n'-Puff Filter</a> page.</li>
35 <li>A new feature called orphan mode provides an automatic, subnet-wide synchronization feature with multiple sources. It provides reliable backup in isolated networks or in pr when Internet sources have become unavailable. See the <a href="orphan.html">Orphan Mode</a> page for further information.</li>
36 <li>This release includes comprehensive packet rate management tools to help reduce the level of spurious network traffic and protect the busiest servers from overload. There is support for the optional Kiss-o'-Death (KoD) packet intended to slow down an abusive client. See the <a href="rate.html">Rate Management and the Kiss-o'-Death Packet</a> page for further information.</li>
38 <li>The OpenSSL cryptographic library has replaced the library formerly available from RSA Laboratories. All cryptographic routines except a version of the MD5 message digest algorithm have been removed from the base distribution. All 128-bit and 160-bit message digests algorithms are now supported for both symmetric key and public key cryptosystems. See the <a href="authentic.html">Authentication Support</a> page for further information and the <a href="authopt.html">Authentication Options</a> page for a list of supported digest algorithms.</li>
39 <li>This release includes support for Autokey public-key cryptography for authenticating public servers to clients, as described in RFC 5906. This support requires the --enable-autokey option when building the distribution, which is the default is OpenSSL is available. The deployment of Autokey subnets is now considerably simpler than in earlier versions. A subnet naming scheme is now available to filter manycast and pool configurations. Additional information about Autokey is on the <a href="autokey.html">Autokey Public Key Authentication</a> page and links from there.</li>
40 <li>The NTP descrete event simulator has been substantially upgraded, now including scenarios with multiple servers and time-sensitive scripts. This allows the NTP algorithms to be tested in an embedded environment with systematic and pseudo-random network delay and oscillator wander distributions. This has been used to verify correct operation under conditions of extreme error and misconfiguration. See the <a href="ntpdsim.html"><tt>ntpdsim</tt> - Network Time Protocol (NTP) simulator</a> page. A technical description and performance analysis is given in the white papers at the <a href="http://www.eecis.udel.edu/~mills/ntp.html">NTP Project Page</a>.</li>
41 <li>NTPv4 includes three new server discovery schemes, which in most applications can avoid per-host configuration altogether. Two of these are based on IP multicast technology, while the remaining one is based on crafted DNS lookups. See the <a href="discover.html">Automatic NTP Configuration Schemes</a> page for further information.</li>
44 <li>The <tt>ntpd</tt> daemon can be operated in a one-time mode similar to <tt>ntpdate</tt>, which program is headed for retirement. See the <a href="ntpd.html"><tt>ntpd</tt> - Network Time Protocol (NTP) daemon</a> page for the new features.</li>
48 <h4 id="change">Changes and Upgrades Since the NTPv3 Version (xntp3-5) </h4>
49 <p>This section summarizes general changes since the publication of RFC-1305. Specific changes made during the code upgrade of 2007-2008 are summarized in <a href="history.html">Historical Notes</a>.</p>
51 <li>If the Basic Socket Interface Extensions for IPv6 (RFC-2553) is detected, support for the IPv6 address family is supported in addition to the default support for the IPv4 address family. In contexts where a host name is expected, a <tt>-4</tt> qualifier preceding the host name forces DNS resolution to the IPv4 namespace, while a <tt>-6</tt> qualifier forces DNS resolution to the IPv6 namespace.</li>
53 <li>In all except a very few cases, all timing intervals are randomized, so that the tendency for NTPv3 to self-synchronize and bunch messages, especially with a large number of configured associations, is minimized.</li>
56 <li>Support for pulse-per-second (PPS) signals has been extended to all drivers as an intrinsic function. Further information is on the <a href="pps.html">Pulse-Per-Second (PPS) Signal Interfacing</a> page. Typical performance with the PPS interface and a fast machine are in the low microseconds.</li>
57 <li>Several small changes have been made to make administration and maintenance more convenience. The entire distribution has been converted to gnu <tt>automake</tt>, which greatly ease the task of porting to new and different programming environments, as well as reduce the incidence of bugs due to improper handling of idiosyncratic kernel functions. Version control is provided by Bitkeeper using an online repository at www.ntp.org. Trouble ticket reporting is provided using Bugzilla. If <tt>ntpd</tt>, is configured with NetInfo support, it will attempt to read its configuration from the NetInfo service if the default <tt>ntp.conf</tt> file cannot be read and no file is specified by the <tt>-c</tt> option. When <tt>ntpd</tt> starts it looks at the value of <tt>umask</tt>, and if zero <tt>ntpd</tt> will set the <tt>umask</tt> to <tt>022</tt>.</li>
60 <p>There are a few things different about this release that have changed since the latest NTP Version 3 release. Following are a few things to worry about:</p>
64 <li>There is a minor change to the reference ID field of the NTP packet header when operating with IPv6 associations. In IPv4 associations this field contains the 32-bit IPv4 address of the server, in order to detect and avoid loops. In IPv6 associations this field contains the first 32-bits of a MD5 hash formed from the IPv6 address. All programs in the distribution have been modified to work with both address families.</li>
65 <li>The <tt>tty_clk</tt> and <tt>ppsclock</tt> pulse-per-second (PPS) line discipline/streams modules are no longer supported. The PPS function is now handled by the <a href="drivers/driver22.html">PPS Clock Discipline</a> driver, which uses the new PPSAPI application program interface adopted by the IETF. Note that the <tt>pps</tt> configuration file command has been obsoleted by the driver. See the <a href="pps.html">Pulse-Per-Second (PPS) Signal Interfacing</a> page for further information.</li>