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      1 <refentry id="tracepath">
      2 
      3 <refmeta>
      4 <refentrytitle>tracepath</refentrytitle>
      5 <manvolnum>8</manvolnum>
      6 <refmiscinfo>iputils-&snapshot;</refmiscinfo>
      7 </refmeta>
      8 
      9 <refnamediv>
     10 <refname>tracepath, tracepath6</refname>
     11 <refpurpose>
     12 traces path to a network host discovering MTU along this path</refpurpose>
     13 </refnamediv>
     14 
     15 <refsynopsisdiv>
     16 <cmdsynopsis>
     17 <command>tracepath</command>
     18 <arg choice="opt">-n</arg>
     19 <arg choice="opt">-b</arg>
     20 <arg choice="opt">-l <replaceable/pktlen/</arg>
     21 <arg choice="opt">-m <replaceable/max_hops/</arg>
     22 <arg choice="opt">-p <replaceable/port/</arg>
     23 <arg choice="req"><replaceable/destination/</arg>
     24 </cmdsynopsis>
     25 </refsynopsisdiv>
     26 
     27 <refsect1><title>DESCRIPTION</title>
     28 <para>
     29 It traces path to <replaceable/destination/ discovering MTU along this path.
     30 It uses UDP port <replaceable/port/ or some random port.
     31 It is similar to <command/traceroute/, only does not require superuser
     32 privileges and has no fancy options.
     33 </para>
     34 
     35 <para>
     36 <command/tracepath6/ is good replacement for <command/traceroute6/
     37 and classic example of application of Linux error queues.
     38 The situation with IPv4 is worse, because commercial
     39 IP routers do not return enough information in ICMP error messages.
     40 Probably, it will change, when they will be updated.
     41 For now it uses Van Jacobson's trick, sweeping a range
     42 of UDP ports to maintain trace history.
     43 </para>
     44 </refsect1>
     45 
     46 <refsect1><title>OPTIONS</title>
     47 <variablelist>
     48 
     49  <varlistentry>
     50   <term><option/-n/</term>
     51   <listitem><para>
     52 Print primarily IP addresses numerically.
     53   </para></listitem>
     54  </varlistentry>
     55 
     56  <varlistentry>
     57   <term><option/-b/</term>
     58   <listitem><para>
     59 Print both of host names and IP addresses.
     60   </para></listitem>
     61  </varlistentry>
     62 
     63  <varlistentry>
     64   <term><option/-l/</term>
     65   <listitem><para>
     66 Sets the initial packet length to <replaceable/pktlen/ instead of
     67 65535 for <command/tracepath/ or 128000 for <command/tracepath6/.
     68   </para></listitem>
     69  </varlistentry>
     70 
     71  <varlistentry>
     72   <term><option/-m</term>
     73   <listitem><para>
     74 Set maximum hops (or maximum TTLs) to <replaceable/max_hops/
     75 instead of 30.
     76   </para></listitem>
     77  </varlistentry>
     78 
     79  <varlistentry>
     80   <term><option/-p/</term>
     81   <listitem><para>
     82 Sets the initial destination port to use.
     83   </para></listitem>
     84  </varlistentry>
     85 </variablelist>
     86 </refsect1>
     87 
     88 <refsect1><title>OUTPUT</title>
     89 <para>
     90 <literallayout>
     91 root@mops:~ # tracepath6 3ffe:2400:0:109::2
     92  1?: [LOCALHOST]                              pmtu 1500
     93  1:  dust.inr.ac.ru                   0.411ms
     94  2:  dust.inr.ac.ru        asymm  1   0.390ms pmtu 1480
     95  2:  3ffe:2400:0:109::2               463.514ms reached
     96      Resume: pmtu 1480 hops 2 back 2
     97 </literallayout>
     98 </para>
     99 
    100 <para>
    101 The first column shows <literal/TTL/ of the probe, followed by colon.
    102 Usually value of <literal/TTL/ is obtained from reply from network,
    103 but sometimes reply does not contain necessary information and
    104 we have to guess it. In this case the number is followed by ?.
    105 </para>
    106 
    107 <para>
    108 The second column shows the network hop, which replied to the probe.
    109 It is either address of router or word <literal/[LOCALHOST]/, if
    110 the probe was not sent to the network.
    111 </para>
    112 
    113 <para>
    114 The rest of line shows miscellaneous information about path to
    115 the correspinding network hop. As rule it contains value of RTT.
    116 Additionally, it can show Path MTU, when it changes.
    117 If the path is asymmetric
    118 or the probe finishes before it reach prescribed hop, difference
    119 between number of hops in forward and backward direction is shown
    120 following keyword <literal/async/. This information is not reliable.
    121 F.e. the third line shows asymmetry of 1, it is because the first probe
    122 with TTL of 2 was rejected at the first hop due to Path MTU Discovery.
    123 </para>
    124 
    125 <para>
    126 The last line summarizes information about all the path to the destination,
    127 it shows detected Path MTU, amount of hops to the destination and our
    128 guess about amount of hops from the destination to us, which can be
    129 different when the path is asymmetric.
    130 </para>
    131 
    132 </refsect1>
    133 
    134 
    135 
    136 
    137 <refsect1><title>SEE ALSO</title>
    138 <para>
    139 <citerefentry><refentrytitle/traceroute/<manvolnum/8/</citerefentry>,
    140 <link linkend="traceroute6">
    141 <citerefentry><refentrytitle/traceroute6/<manvolnum/8/</citerefentry></link>,
    142 <link linkend="ping">
    143 <citerefentry><refentrytitle/ping/<manvolnum/8/</citerefentry></link>.
    144 </para>
    145 </refsect1>
    146 
    147 <refsect1><title>AUTHOR</title>
    148 <para>
    149 <command/tracepath/ was written by
    150 <ulink url="mailto:kuznet (a] ms2.inr.ac.ru">Alexey Kuznetsov
    151 &lt;kuznet (a] ms2.inr.ac.ru&gt;</ulink>.
    152 </para>
    153 </refsect1>
    154 
    155 <refsect1><title>SECURITY</title>
    156 <para>
    157 No security issues.
    158 </para>
    159 <para>
    160 This lapidary deserves to be elaborated.
    161 <command/tracepath/ is not a privileged program, unlike
    162 <command/traceroute/, <command/ping/ and other beasts of this kind.
    163 <command/tracepath/ may be executed by everyone who has some access
    164 to network, enough to send UDP datagrams to investigated destination
    165 using given port.
    166 </para>
    167 </refsect1>
    168 
    169 <refsect1><title>AVAILABILITY</title>
    170 <para>
    171 <command/tracepath/ is part of <filename/iputils/ package
    172 and the latest versions are  available in source form at
    173 <ulink url="http://www.skbuff.net/iputils/iputils-current.tar.bz2">
    174 http://www.skbuff.net/iputils/iputils-current.tar.bz2</ulink>.
    175 </para>
    176 </refsect1>
    177 
    178 <![IGNORE[
    179 <refsect1><title>COPYING</title>
    180 <para>
    181 <literallayout>
    182 This documentation is free software; you can redistribute
    183 it and/or modify it under the terms of the GNU General Public
    184 License Version 2.
    185 
    186 This program is distributed in the hope that it will be
    187 useful, but WITHOUT ANY WARRANTY; without even the implied
    188 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
    189 See the GNU General Public License for more details.
    190  
    191 For more details see the file COPYING in the source
    192 distribution of Linux kernel of version 2.4.
    193 </literallayout>
    194 </para>
    195 </refsect1>
    196 ]]>
    197 
    198 
    199 
    200 
    201 </refentry>
    202