2000-03-29 16:38:44 +04:00
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<html><head><title>
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Configuration Options
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</title></head><body><h3>
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Configuration Options
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</h3><hr>
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<h4>Configuration Support</h4>
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2000-04-22 18:51:59 +04:00
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<p>Following is a description of the configuration commands in NTPv4.
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These commands have the same basic functions as in NTPv3 and in some
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cases new functions and new arguments. There are two classes of
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commands, configuration commands that configure a persistent association
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with a remote server or peer or reference clock, and auxilliary commands
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that specify environmental variables that control various related
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operations.
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<h4>Configuration Commands</h4>
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<p>The various modes are determined by the command keyword and the type
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of the required IP address. Addresses are classed by type as (s) a
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remote server or peer (IP class A, B and C), (b) the broadcast address
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of a local interface, (m) a multicast address (IP class D), or (r) a
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reference clock address (127.127.x.x). Note that some options are not
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supported by all these commands while autokey and burst modes are
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supported by these commands,
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their effect in some weird mode combinations can be meaningless
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or even destructive.
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<dl>
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<dt><tt>peer <i>address</i> [key <i>key</i> | autokey | publickey
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<i>keyfile</i>] [burst] [version <i>version</i>] [prefer] [minpoll
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<i>minpoll</i>] [maxpoll <i>maxpoll</i>]</tt></dt>
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<p><dt><tt>server <i>address</i> [key <i>key</i> | autokey | publickey
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<i>keyfile</i>] [burst] [version <i>version</i>] [prefer] [minpoll
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<i>minpoll</i>] [maxpoll <i>maxpoll</i>] [publickey
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<i>keyfile</i>]</tt></dt>
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<p><dt><tt>broadcast <i>address</i> [key <i>key</i> | autokey] [burst]
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[version <i>version</i>] [minpoll <i>minpoll</i>] [maxpoll
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<i>maxpoll</i>] [ttl <i>ttl</i>]</tt></dt>
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<p><dt><tt>manycastclient <i>address</i> [key <i>key</i> | autokey |
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publickey <i>keyfile</i>] [burst] [version <i>version</i>] [minpoll
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<i>minpoll</i> [maxpoll <i>maxpoll</i>] [ttl <i>ttl</i>] [publickey
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<i>file</i>]</tt></dt>
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<p><<dd>These four commands specify the time server name or address to
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be used and the mode in which to operate. The <i>address</i> can be
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either a DNS name or a IP address in dotted-quad notation. Additional
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information on association behavior can be found in the <a
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href="assoc.htm">Association Management</a> page.</dd>
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<dd><dl>
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<dt><tt>server</tt></dt>
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<dd>For type s and r addresses, this operates as the NTPv3 server
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command, which mobilizes a persistent client mode association. The
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<tt>server</tt> command specifies that the local server is to operate in
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client mode with the specified remote server. In this mode, the local
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server can be synchronized to the remote server, but the remote server
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can never be synchronized to the local server.</dd>
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<dt><tt>peer</tt></dt>
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<dd>For type s addresses (only), this operates as the current <tt>peer
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</tt>command, which mobilizes a persistent symmetric-active mode
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association, except that additional modes are available. This command
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should NOT be used for type <tt>b</tt>, <tt>m</tt> or <tt>r</tt>
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addresses.</dd>
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<p><dd>The <tt>peer</tt> command specifies that the local server is to
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operate in symmetric active mode with the remote server. In this mode,
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the local server can be synchronized to the remote server and, in
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addition, the remote server can be synchronized by the local server.
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This is useful in a network of servers where, depending on various
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failure scenarios, either the local or remote server may be the better
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source of time.</dd>
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<dt><tt>broadcast</tt></dt>
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<dd>For type <tt>b</tt> and <tt>m</tt> addresses (only), this operates
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as the current NTPv3 <tt>broadcast </tt>command, which mobilizes a
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persistent broadcast mode association, except that additional modes are
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available. Multiple commands can be used to specify multiple local
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broadcast interfaces (subnets) and/or multiple multicast groups. Note
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that local broadcast messages go only to the interface associated with
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the subnet specified, but multicast messages go to all interfaces. In
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the current implementation, the source address used for these messages
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is the Unix host default address.</dd>
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<p><dd>In broadcast mode, the local server sends periodic broadcast
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messages to a client population at the <i><tt>address</tt></i>specified,
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which is usually the broadcast address on (one of) the local network(s)
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or a multicast address assigned to NTP. The IANA has assigned the
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multicast group address 224.0.1.1 exclusively to NTP, but other
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nonconflicting addresses can be used to contain the messages within
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administrative boundaries.. Ordinarily, this specification applies only
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to the local server operating as a sender; for operation as a broadcast
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client, see the <tt>broadcastclient</tt> or <tt>multicastclient</tt>
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commands below.</dd>
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<dt><tt>manycastclient</tt>
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<dd>For type <tt>m</tt> addresses (only), this mobilizes a manycast
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client-mode association for the multicast address specified. In this
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case a specific address must be supplied which matches the address used
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on the <tt>manycastserver </tt>command for the designated manycast
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servers. The NTP multicast address 224.0.1.1 assigned by the IANA should
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NOT be used, unless specific means are taken to avoid spraying large
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areas of the Internet with these messages and causing a possibly massive
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implosion of replies at the sender. </dd>
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<p><dd>The <tt>manycast </tt>command specifies that the local server is
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to operate in client mode with the remote server that are discovered as
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the result of broadcast/multicast messages. The client broadcasts a
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request message to the group address associated with the specified
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<i><tt>address </tt></i>and specifically enabled servers respond to
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these messages. The client selects the servers providing the best time
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and continues as with the <tt>server </tt>command. The remaining servers
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are discarded as if never heard.</dd>
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</dl>
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<dd>Options</dd>
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<dl><dd>
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<dt><tt>autokey</tt></dt>
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<dd>All packets sent to and received from the server or peer are to
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include authentication fields encrypted using the autokey scheme
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described in the <a href=authopt.htm>Authentication Options</a>
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page.</dd>
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<dt><tt>burst</tt></dt>
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<dd>At each poll interval, send a burst of eight packets spaced, instead
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of the usual one.</dd>
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<dt><tt>key </tt><i><tt>key</tt></i></dt>
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<dd>All packets sent to and received from the server or peer are to
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include authentication fields encrypted using the specified <i>key</i>
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identifier with values from 1 to 65534, inclusive. The default is to
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include no encryption field.</dd>
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<dt><tt>minpoll <i>minpoll</i></tt>
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<br><tt>maxpoll <i>maxpoll</i></tt>
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<dd>These options specify the minimum and maximum polling intervals for
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NTP messages, in seconds to the power of two. The default range is 6 (64
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s) to 10 (1,024 s). The allowable range is 4 (16 s) to 17 (36.4 h)
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inclusive.</dd>
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<dt><tt>prefer</tt></dt>
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<dd>Marks the server as preferred. All other things being equal, this
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host will be chosen for synchronization among a set of correctly
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operating hosts. See the <a href="prefer.htm">Mitigation Rules and the
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<tt>prefer</tt> Keyword </a>page for further information.</dd>
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<DT><TT>publickey <I>file</I></TT></DT>
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<DD>This command requires the NTP daemon build process be configured
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with the RSA library. The command specifies the name of the public key
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file for the server or peer. The default name for this file is
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<tt>ntpkey_<i>host</i></tt>, where <i>host</i> is the DNS canonical name
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of the server or peer. See the <a href=authopt.htm>Authentication
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Options</a> page for further information.</dd>
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<dt><tt>ttl <i>ttl</i></tt></dt>
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<dd>This option is used only with broadcast mode. It specifies the
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time-to-live <i><tt>ttl</tt></i> to use on multicast packets. Selection
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of the proper value, which defaults to 127, is something of a black art
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and must be coordinated with the network administrator.</dd>
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<dt><tt>version <i>version</i></tt></dt>
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<dd>Specifies the version number to be used for outgoing NTP packets.
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Versions 1-4 are the choices, with version 4 the default.</dd>
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</dl></dd></dl></dd>
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<h4>Auxilliary Commands</h4>
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<dl>
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<dt><tt>broadcastclient</tt>
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<dd>This command directs the local server to listen for and respond to
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broadcast messages received on any local interface. Upon hearing a
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broadcast message for the first time, the local server measures the
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nominal network delay using a brief client/server exchange with the
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remote server, then enters the broadcastclient mode, in which it listens
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for and synchronizes to succeeding broadcast messages. Note that, in
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order to avoid accidental or malicious disruption in this mode, both the
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local and remote servers should operate using authentication and the
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same trusted key and key identifier.</dd>
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<dt><tt>manycastserver <i>address</i> [...]</tt>
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<dd>This command directs the local server to listen for and respond to
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broadcast messages received on any local interface, and in addition
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enables the server to respond to client mode messages to the multicast
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group address(es) (type m) specified. At least one address is required,
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but The NTP multicast address 224.0.1.1 assigned by the IANA should NOT
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be used, unless specific means are taken to limit the span of the reply
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and avoid a possibly massive implosion at the original sender.</dd>
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<dt><tt>multicastclient [<i>address</i>] [...]</tt>
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<dd>This command directs the local server to listen for multicast
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messages at the group address(es) of the global network. The default
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address is that assigned by the Numbers Czar to NTP (224.0.1.1). This
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command operates in the same way as the <tt>broadcastclient</tt>
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command, but uses IP multicasting. Support for this command requires
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multicast kernel support.</dd>
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2000-03-29 16:38:44 +04:00
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</dl>
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2000-04-22 18:51:59 +04:00
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<h4>Bugs</h4>
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<p>The syntax checking is not picky; some combinations of ridiculous and
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even hilarious options and modes may not be detected.
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2000-04-22 20:46:49 +04:00
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<hr><a href=index.htm>Home</a><address><a
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href=mailto:mills@udel.edu> David L. Mills <mills@udel.edu></a>
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</address></a></body></html>
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