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="req"><replaceable/destination/</arg> 19<arg choice="opt"><replaceable/port/</arg> 20</cmdsynopsis> 21</refsynopsisdiv> 22 23<refsect1><title>DESCRIPTION</title> 24<para> 25It traces path to <replaceable/destination/ discovering MTU along this path. 26It uses UDP port <replaceable/port/ or some random port. 27It is similar to <command/traceroute/, only does not not require superuser 28privileges and has no fancy options. 29</para> 30 31<para> 32<command/tracepath6/ is good replacement for <command/traceroute6/ 33and classic example of application of Linux error queues. 34The situation with <command/tracepath/ is worse, because commercial 35IP routers do not return enough information in icmp error messages. 36Probably, it will change, when they will be updated. 37For now it uses Van Jacobson's trick, sweeping a range 38of UDP ports to maintain trace history. 39</para> 40</refsect1> 41 42<refsect1><title>OUTPUT</title> 43<para> 44<literallayout> 45root@mops:~ # tracepath6 3ffe:2400:0:109::2 46 1?: [LOCALHOST] pmtu 1500 47 1: dust.inr.ac.ru 0.411ms 48 2: dust.inr.ac.ru asymm 1 0.390ms pmtu 1480 49 2: 3ffe:2400:0:109::2 463.514ms reached 50 Resume: pmtu 1480 hops 2 back 2 51</literallayout> 52</para> 53 54<para> 55The first column shows <literal/TTL/ of the probe, followed by colon. 56Usually value of <literal/TTL/ is obtained from reply from network, 57but sometimes reply does not contain necessary information and 58we have to guess it. In this case the number is followed by ?. 59</para> 60 61<para> 62The second column shows the network hop, which replied to the probe. 63It is either address of router or word <literal/[LOCALHOST]/, if 64the probe was not sent to the network. 65</para> 66 67<para> 68The rest of line shows miscellaneous information about path to 69the correspinding hetwork hop. As rule it contains value of RTT. 70Additionally, it can show Path MTU, when it changes. 71If the path is asymmetric 72or the probe finishes before it reach prescribed hop, difference 73between number of hops in forward and backward direction is shown 74folloing keyword <literal/async/. This information is not reliable. 75F.e. the third line shows asymmetry of 1, it is because the first probe 76with TTL of 2 was rejected at the first hop due to Path MTU Discovery. 77</para> 78 79<para> 80Te last line summarizes information about all the path to the destination, 81it shows detected Path MTU, amount of hops to the destination and our 82guess about amount of hops from the destination to us, which can be 83different when the path is asymmetric. 84</para> 85 86</refsect1> 87 88 89 90 91<refsect1><title>SEE ALSO</title> 92<para> 93<citerefentry><refentrytitle/traceroute/<manvolnum/8/</citerefentry>, 94<link linkend="traceroute6"> 95<citerefentry><refentrytitle/traceroute6/<manvolnum/8/</citerefentry></link>, 96<link linkend="ping"> 97<citerefentry><refentrytitle/ping/<manvolnum/8/</citerefentry></link>. 98</para> 99</refsect1> 100 101<refsect1><title>AUTHOR</title> 102<para> 103<command/tracepath/ was written by 104<ulink url="mailto:kuznet@ms2.inr.ac.ru">Alexey Kuznetsov 105<kuznet@ms2.inr.ac.ru></ulink>. 106</para> 107</refsect1> 108 109<refsect1><title>SECURITY</title> 110<para> 111No security issues. 112</para> 113<para> 114This lapidary deserves to be elaborated. 115<command/tracepath/ is not a privileged program, unlike 116<command/traceroute/, <command/ping/ and other beasts of this kind. 117<command/tracepath/ may be executed by everyone who has some access 118to network, enough to send UDP datagrams to investigated destination 119using given port. 120</para> 121</refsect1> 122 123<refsect1><title>AVAILABILITY</title> 124<para> 125<command/tracepath/ is part of <filename/iputils/ package 126and the latest versions are available in source form from anonymous ftp 127<ulink url="ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz"> 128ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz</ulink>. 129</para> 130</refsect1> 131 132<![IGNORE[ 133<refsect1><title>COPYING</title> 134<para> 135<literallayout> 136This documentation is free software; you can redistribute 137it and/or modify it under the terms of the GNU General Public 138License Version 2. 139 140This program is distributed in the hope that it will be 141useful, but WITHOUT ANY WARRANTY; without even the implied 142warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 143See the GNU General Public License for more details. 144 145For more details see the file COPYING in the source 146distribution of Linux kernel of version 2.4. 147</literallayout> 148</para> 149</refsect1> 150]]> 151 152 153 154 155</refentry> 156