1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2<html> 3<head> 4<meta http-equiv="content-type" content="text/html;charset=iso-8859-1"> 5<meta name="generator" content="HTML Tidy, see www.w3.org"> 6<title>Server Options</title> 7<link href="scripts/style.css" type="text/css" rel="stylesheet"> 8</head> 9<body> 10<h3>Server Options</h3> 11<img src="pic/boom3a.gif" alt="gif" align="left"><a href="http://www.eecis.udel.edu/~mills/pictures.html">from <i>Pogo</i>, 12Walt Kelly</a> 13<p>The chicken is getting configuration advice.</p> 14<p>Last update: 15 <!-- #BeginDate format:En2m -->25-Nov-2009 4:46<!-- #EndDate --> 16</p> 17<br clear="left"> 18<h4>Related Links</h4> 19<script type="text/javascript" language="javascript" src="scripts/command.txt"></script> 20<script type="text/javascript" language="javascript" src="scripts/confopt.txt"></script> 21<h4>Table of Contents</h4> 22<ul> 23 <li class="inline"><a href="#cfg">Configuration Commands</a></li> 24 <li class="inline"><a href="#opt">Command Options</a></li> 25 <li class="inline"><a href="#aux">Auxilliary Commands</a></li> 26 <li class="inline"><a href="#bug">Bugs</a></li> 27</ul> 28<hr> 29<p>Following is a description of the configuration commands in NTPv4. There are 30 two classes of commands, configuration commands that configure an association 31 with a remote server, peer or reference clock, and auxilliary commands that 32 specify environmental variables that control various related operations. </p> 33<p>The various modes described on the <a href="assoc.html">Association Management</a> page 34 are determined by the command keyword and the DNS name or IP address. Addresses 35 are classed by type as (s) a remote server or peer (IPv4 class A, B and C), 36 (b) the IP broadcast address of a local interface, (m) a multicast address (IPv4 37 class D), or (r) a reference clock address (127.127.x.x). For type m addresses 38 the IANA has assigned the multicast group address IPv4 224.0.1.1 and IPv6 ff05::101 39 (site local) exclusively to NTP, but other nonconflicting addresses can be used. </p> 40<p>If the Basic Socket Interface Extensions for IPv6 (RFC-2553) is detected, 41 support for the IPv6 address family is generated in addition to the default 42 IPv4 address family. IPv6 addresses can be identified by the presence of colons ":" in 43 the address field. IPv6 addresses can be used almost everywhere where IPv4 addresses 44 can be used, with the exception of reference clock addresses, which are always 45 IPv4. Note that in contexts where a host name is expected, a <tt>-4</tt> qualifier 46 preceding the host name forces DNS resolution to the IPv4 namespace, while a <tt>-6</tt> qualifier 47 forces DNS resolution to the IPv6 namespace.</p> 48<h4 id="cfg">Configuration Commands</h4> 49<dl> 50 <dt id="server"><tt>server <i>address</i> [options ...]</tt><br> 51 <tt>peer <i>address</i> [options ...]</tt><br> 52 <tt>broadcast <i>address</i> [options ...]</tt><br> 53 <tt>manycastclient <i>address</i> [options ...]</tt><br> 54 <tt>pool <i>address</i> [options ...]</tt><br> 55 <tt>unpeer [<i>address</i> | <i>associd</i>]</tt></dt> 56 <dd>These commands specify the time server name or address to be used and the 57 mode in which to operate. The <i>address</i> can be either a DNS name or a 58 IPv4 or IPv6 address in standard notation. In general, multiple commands of 59 each type can be used for different server and peer addresses or multicast 60 groups. 61 <dl> 62 <dt><tt>server</tt></dt> 63 <dd>For type s and r addresses (only), this command mobilizes a persistent 64 client mode association with the specified remote server or local reference 65 clock. If the <tt>preempt</tt> flag is specified, a preemptable client mode 66 association is mobilized instead.</dd> 67 <dt><tt>peer</tt></dt> 68 <dd>For type s addresses (only), this command mobilizes a persistent symmetric-active 69 mode association with the specified remote peer.</dd> 70 <dt><tt>broadcast</tt></dt> 71 <dd>For type b and m addressees (only), this command mobilizes a persistent 72 broadcast or multicast server mode association. Note that type 73 b messages go only to the interface specified, but type m messages go to 74 all interfaces.</dd> 75 <dt><tt>manycastclient</tt></dt> 76 <dd>For type m addresses (only), this command mobilizes a manycast client 77 mode association for the multicast group address specified. In this mode 78 the address must match the address specified on the <tt>manycastserver</tt> command 79 of one or more designated manycast servers.</dd> 80 <dt><tt>pool</tt></dt> 81 <dd>For type s messages (only) this command mobilizes a client mode association 82 for servers implementing the pool automatic server discovery scheme described 83 on the <a href="assoc.html">Association Management</a> page. The address 84 is a DNS name in the form <tt><i>area</i>.pool.ntp.org</tt>, where <tt><i>area</i></tt> is 85 a qualifier designating the server geographic area such as <tt>us</tt> or <tt>europe</tt>.</dd> 86 <dt><tt>unpeer</tt></dt> 87 <dd>This command removes a previously configured association. An address or association ID can 88 be used to identify the association. Either an IP address or DNS name can be used. This 89 command is most useful when supplied via <tt><a href="ntpq.html">ntpq</a></tt> runtime 90 configuration commands <tt>:config</tt> and <tt>config-from-file</tt>.</dd> 91 </dl></dd> 92</dl> 93<h4 id="opt">Command Options</h4> 94<dl> 95 <dt><tt>autokey</tt></dt> 96 <dd>Send and receive packets authenticated by the Autokey scheme described 97 in the <a href="authopt.html">Authentication Options</a> page. This option 98 is mutually exclusive with the <tt>key</tt> option.</dd> 99 <dt><tt>burst</tt></dt> 100 <dd>When the server is reachable, send a burst of eight packets instead of the 101 usual one. The packet spacing is normally 2 s; however, the spacing between 102 the first and second packets can be changed with the <a href="miscopt.html"><tt>calldelay</tt></a> command 103 to allow additional time for a modem or ISDN call to complete. This option 104 is valid only with the <tt>server</tt> command and type s addressesa. 105 It is a recommended option when the <tt>maxpoll</tt> option is greater than 106 10 (1024 s).</dd> 107 <dt><tt>iburst</tt></dt> 108 <dd>When the server is unreachable, send a burst of eight packets instead of 109 the usual one. The packet spacing is normally 2 s; however, the spacing between 110 the first and second packets can be changed with the <a href="miscopt.html"><tt>calldelay</tt></a> command 111 to allow additional time for a modem or ISDN call to complete. This option 112 is valid only with the <tt>server</tt> command and type s addresses. It is 113 a recommended option with this command.</dd> 114 <dt><tt>key</tt> <i><tt>key</tt></i></dt> 115 <dd>Send and receive packets authenticated by the symmetric key scheme described 116 in the <a href="authopt.html">Authentication Options</a> page. 117 The <i><tt>key</tt></i> specifies the key identifier with values from 1 to 118 65534, inclusive. This option is mutually exclusive with the <tt>autokey</tt> option.</dd> 119 <dt><tt>minpoll <i>minpoll<br> 120 </i></tt><tt>maxpoll <i>maxpoll</i></tt></dt> 121 <dd>These options specify the minimum and maximum poll intervals for NTP messages, 122 in seconds as a power of two. The maximum poll interval defaults to 10 123 (1024 s), but can be increased by the <tt>maxpoll</tt> option to an upper limit 124 of 17 (36 h). The minimum poll interval defaults to 6 (64 s), but can 125 be decreased by the <tt>minpoll</tt> option to a lower limit of 3 (8 s).</dd> 126 <dt><tt>mode <i>option</i></tt></dt> 127 <dd>Pass the <tt><i>option</i></tt> to a reference clock driver, where <tt><i>option</i></tt> is 128 an integer in the range from 0 to 255, inclusive. This option is valid 129 only with type r addresses.</dd> 130 <dt><tt>noselect</tt></dt> 131 <dd>Marks the server or peer to be ignored by the selection algorithm but visible 132 to the monitoring program. This option is ignored with the <tt>broadcast</tt> command.</dd> 133 <dt><tt>preempt</tt></dt> 134 <dd>Specifies the association as preemptable rather than the default persistent. 135 This option is ignored with the <tt>broadcast</tt> command and is most useful 136 with the <tt>manycastclient</tt> and <tt>pool</tt> commands.</dd> 137 <dt><tt>prefer</tt></dt> 138 <dd>Mark the server as preferred. All other things being equal, this host will 139 be chosen for synchronization among a set of correctly operating hosts. See 140 the <a href="prefer.html">Mitigation Rules and the <tt>prefer</tt> Keyword</a> page 141 for further information. This option is valid only with the <tt>server</tt> and <tt>peer</tt> commands.</dd> 142 <dt><tt>true</tt></dt> 143 <dd>Mark the association to assume truechimer status; that is, always survive 144 the selection and clustering algorithms. This option can be used with any association, 145 but is most useful for reference clocks with large jitter on the serial port 146 and precision pulse-per-second (PPS) signals. Caution: this option defeats 147 the algorithms designed to cast out falsetickers and can allow these sources 148 to set the system clock. This option is valid only with the <tt>server</tt> and <tt>peer</tt> commands.</dd> 149 <dt><tt>ttl <i>ttl</i></tt></dt> 150 <dd>This option specifies the time-to-live <i><tt>ttl</tt></i> for the <tt>broadcast</tt> command 151 and the maximum <i><tt>ttl</tt></i> for the expanding ring search used by the <tt>manycastclient</tt> command. 152 Selection of the proper value, which defaults to 127, is something of a black art and should be coordinated with the network administrator. This option is invalid with type r addresses.</dd> 153 <dt><tt>version <i>version</i></tt></dt> 154 <dd>Specifies the version number to be used f 155or outgoing NTP packets. Versions 156 1-4 are the choices, with version 4 the default.</dd> 157 <dt><tt>xleave</tt></dt> 158 <dd>Operate in interleaved mode (symmetric and broadcast modes only). (see <a href="xleave.html">NTP 159 Interleaved Modes</a>)</dd> 160</dl> 161<h4 id="aux">Auxilliary Commands</h4> 162<dl> 163 <dt id="broadcastclient"><tt>broadcastclient</tt></dt> 164 <dd>Enable reception of broadcast server messages to any local interface (type 165 b address). Ordinarily, upon receiving a broadcast message for the first 166 time, the broadcast client measures the nominal server propagation delay using 167 a brief client/server exchange, after which it continues in listen-only mode. 168 If a nonzero value is specified in the <tt>broadcastdelay</tt> command, the 169 value becomes the delay and the volley is not executed. Note: the <tt>novolley</tt> option 170 has been deprecated for future enhancements. Note that, in order to avoid 171 accidental or malicious disruption in this mode, both the server and client 172 should operate using symmetric key or public key authentication as described 173 in the <a href="authopt.html">Authentication 174 Options</a> page. Note that the <tt>novolley</tt> keyword is incompatible with 175 public key authentication.</dd> 176 <dt id="manycastserver"><tt>manycastserver <i>address</i> [...]</tt></dt> 177 <dd>Enable reception of manycast client messages (type m)to the multicast group 178 address(es) (type m) specified. At least one address is required. Note that, 179 in order to avoid accidental or malicious disruption, both the server and client 180 should operate using symmetric key or public key authentication as described 181 in the <a href="authopt.html">Authentication Options</a> page.</dd> 182 <dt id="multicastclient"><tt>multicastclient <i>address</i> [...]</tt></dt> 183 <dd>Enable reception of multicast server messages to the multicast group address(es) 184 (type m) specified. Upon receiving a message for the first time, the multicast 185 client measures the nominal server propagation delay using a brief client/server 186 exchange with the server, then enters the broadcast client mode, in which it 187 synchronizes to succeeding multicast messages. Note that, in order to avoid 188 accidental or malicious disruption in this mode, both the server and client 189 should operate using symmetric key or public key authentication as described 190 in the <a href="authopt.html">Authentication Options</a> page.</dd> 191</dl> 192<h4 id="bug">Bugs</h4> 193<p>The syntax checking is not picky; some combinations of ridiculous and even 194 hilarious options and modes may not be detected.</p> 195<hr> 196<script type="text/javascript" language="javascript" src="scripts/footer.txt"></script> 197</body> 198</html> 199
