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105 lines
3.8 KiB
105 lines
3.8 KiB
9 years ago
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.\" This manpage has been automatically generated by docbook2man
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.\" from a DocBook document. This tool can be found at:
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.\" <http://shell.ipoline.com/~elmert/comp/docbook2X/>
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.\" Please send any bug reports, improvements, comments, patches,
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.\" etc. to Steve Cheng <steve@ggi-project.org>.
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.TH "TRACEPATH" "8" "07 May 2014" "iputils-121221" "System Manager's Manual: iputils"
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.SH NAME
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tracepath, tracepath6 \- traces path to a network host discovering MTU along this path
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.SH SYNOPSIS
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\fBtracepath\fR [\fB-n\fR] [\fB-b\fR] [\fB-l \fIpktlen\fB\fR] [\fB-m \fImax_hops\fB\fR] [\fB-p \fIport\fB\fR] \fB\fIdestination\fB\fR
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.SH "DESCRIPTION"
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.PP
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It traces path to \fIdestination\fR discovering MTU along this path.
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It uses UDP port \fIport\fR or some random port.
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It is similar to \fBtraceroute\fR, only does not require superuser
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privileges and has no fancy options.
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.PP
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\fBtracepath6\fR is good replacement for \fBtraceroute6\fR
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and classic example of application of Linux error queues.
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The situation with IPv4 is worse, because commercial
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IP routers do not return enough information in ICMP error messages.
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Probably, it will change, when they will be updated.
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For now it uses Van Jacobson's trick, sweeping a range
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of UDP ports to maintain trace history.
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.SH "OPTIONS"
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.TP
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\fB-n\fR
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Print primarily IP addresses numerically.
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.TP
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\fB-b\fR
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Print both of host names and IP addresses.
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.TP
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\fB-l\fR
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Sets the initial packet length to \fIpktlen\fR instead of
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65535 for \fBtracepath\fR or 128000 for \fBtracepath6\fR.
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.TP
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\fB-m/term> \fR
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Set maximum hops (or maximum TTLs) to \fImax_hops\fR
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instead of 30.
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.TP
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\fB-p\fR
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Sets the initial destination port to use.
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.SH "OUTPUT"
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.PP
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.nf
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root@mops:~ # tracepath6 3ffe:2400:0:109::2
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1?: [LOCALHOST] pmtu 1500
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1: dust.inr.ac.ru 0.411ms
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2: dust.inr.ac.ru asymm 1 0.390ms pmtu 1480
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2: 3ffe:2400:0:109::2 463.514ms reached
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Resume: pmtu 1480 hops 2 back 2
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.fi
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.PP
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The first column shows TTL of the probe, followed by colon.
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Usually value of TTL is obtained from reply from network,
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but sometimes reply does not contain necessary information and
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we have to guess it. In this case the number is followed by ?.
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.PP
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The second column shows the network hop, which replied to the probe.
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It is either address of router or word [LOCALHOST], if
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the probe was not sent to the network.
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.PP
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The rest of line shows miscellaneous information about path to
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the correspinding network hop. As rule it contains value of RTT.
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Additionally, it can show Path MTU, when it changes.
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If the path is asymmetric
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or the probe finishes before it reach prescribed hop, difference
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between number of hops in forward and backward direction is shown
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following keyword async. This information is not reliable.
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F.e. the third line shows asymmetry of 1, it is because the first probe
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with TTL of 2 was rejected at the first hop due to Path MTU Discovery.
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.PP
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The last line summarizes information about all the path to the destination,
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it shows detected Path MTU, amount of hops to the destination and our
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guess about amount of hops from the destination to us, which can be
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different when the path is asymmetric.
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.SH "SEE ALSO"
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.PP
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\fBtraceroute\fR(8),
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\fBtraceroute6\fR(8),
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\fBping\fR(8).
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.SH "AUTHOR"
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.PP
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\fBtracepath\fR was written by
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Alexey Kuznetsov
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<kuznet@ms2.inr.ac.ru>.
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.SH "SECURITY"
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.PP
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No security issues.
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.PP
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This lapidary deserves to be elaborated.
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\fBtracepath\fR is not a privileged program, unlike
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\fBtraceroute\fR, \fBping\fR and other beasts of this kind.
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\fBtracepath\fR may be executed by everyone who has some access
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to network, enough to send UDP datagrams to investigated destination
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using given port.
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.SH "AVAILABILITY"
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.PP
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\fBtracepath\fR is part of \fIiputils\fR package
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and the latest versions are available in source form at
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http://www.skbuff.net/iputils/iputils-current.tar.bz2.
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