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&lt;kuznet@ms2.inr.ac.ru&gt;</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