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&lt;kuznet@ms2.inr.ac.ru&gt;</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]]>
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155</refentry>
156