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> 12traces 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> 29It traces path to <replaceable/destination/ discovering MTU along this path. 30It uses UDP port <replaceable/port/ or some random port. 31It is similar to <command/traceroute/, only does not require superuser 32privileges and has no fancy options. 33</para> 34 35<para> 36<command/tracepath6/ is good replacement for <command/traceroute6/ 37and classic example of application of Linux error queues. 38The situation with IPv4 is worse, because commercial 39IP routers do not return enough information in ICMP error messages. 40Probably, it will change, when they will be updated. 41For now it uses Van Jacobson's trick, sweeping a range 42of 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> 52Print primarily IP addresses numerically. 53 </para></listitem> 54 </varlistentry> 55 56 <varlistentry> 57 <term><option/-b/</term> 58 <listitem><para> 59Print both of host names and IP addresses. 60 </para></listitem> 61 </varlistentry> 62 63 <varlistentry> 64 <term><option/-l/</term> 65 <listitem><para> 66Sets the initial packet length to <replaceable/pktlen/ instead of 6765535 for <command/tracepath/ or 128000 for <command/tracepath6/. 68 </para></listitem> 69 </varlistentry> 70 71 <varlistentry> 72 <term><option/-m</term> 73 <listitem><para> 74Set maximum hops (or maximum TTLs) to <replaceable/max_hops/ 75instead of 30. 76 </para></listitem> 77 </varlistentry> 78 79 <varlistentry> 80 <term><option/-p/</term> 81 <listitem><para> 82Sets 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> 91root@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> 101The first column shows <literal/TTL/ of the probe, followed by colon. 102Usually value of <literal/TTL/ is obtained from reply from network, 103but sometimes reply does not contain necessary information and 104we have to guess it. In this case the number is followed by ?. 105</para> 106 107<para> 108The second column shows the network hop, which replied to the probe. 109It is either address of router or word <literal/[LOCALHOST]/, if 110the probe was not sent to the network. 111</para> 112 113<para> 114The rest of line shows miscellaneous information about path to 115the correspinding network hop. As rule it contains value of RTT. 116Additionally, it can show Path MTU, when it changes. 117If the path is asymmetric 118or the probe finishes before it reach prescribed hop, difference 119between number of hops in forward and backward direction is shown 120following keyword <literal/async/. This information is not reliable. 121F.e. the third line shows asymmetry of 1, it is because the first probe 122with TTL of 2 was rejected at the first hop due to Path MTU Discovery. 123</para> 124 125<para> 126The last line summarizes information about all the path to the destination, 127it shows detected Path MTU, amount of hops to the destination and our 128guess about amount of hops from the destination to us, which can be 129different 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@ms2.inr.ac.ru">Alexey Kuznetsov 151<kuznet@ms2.inr.ac.ru></ulink>. 152</para> 153</refsect1> 154 155<refsect1><title>SECURITY</title> 156<para> 157No security issues. 158</para> 159<para> 160This 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 164to network, enough to send UDP datagrams to investigated destination 165using given port. 166</para> 167</refsect1> 168 169<refsect1><title>AVAILABILITY</title> 170<para> 171<command/tracepath/ is part of <filename/iputils/ package 172and the latest versions are available in source form at 173<ulink url="http://www.skbuff.net/iputils/iputils-current.tar.bz2"> 174http://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> 182This documentation is free software; you can redistribute 183it and/or modify it under the terms of the GNU General Public 184License Version 2. 185 186This program is distributed in the hope that it will be 187useful, but WITHOUT ANY WARRANTY; without even the implied 188warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 189See the GNU General Public License for more details. 190 191For more details see the file COPYING in the source 192distribution of Linux kernel of version 2.4. 193</literallayout> 194</para> 195</refsect1> 196]]> 197 198 199 200 201</refentry> 202