external/bsd/ntp/dist/html/confopt.html

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  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>,
  12 Walt 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>
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  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 &quot;:&quot; 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
 155 or 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>
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