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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OUTPUT | HANDLING ERRORS | SEE ALSO | AUTHOR | SECURITY | AVAILABILITY | COLOPHON |
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TRACEPATH(8) iputils TRACEPATH(8)
tracepath - traces path to a network host discovering MTU along
this path
tracepath [-4] [-6] [-n] [-b] [-l pktlen] [-m max_hops] [-p port]
[-V] {destination}
It traces the network path to destination discovering MTU along
this path. It uses UDP port port or some random port. It is
similar to traceroute. However, it does not require superuser
privileges and has no fancy options.
tracepath -6 is a good replacement for traceroute6 and classic
example of application of Linux error queues. The situation with
IPv4 is worse, because commercial IP routers do not return enough
information in ICMP error messages. Probably, it will change, when
they are updated. For now it uses Van Jacobson's trick, sweeping a
range of UDP ports to maintain trace history.
-4
Use IPv4 only.
-6
Use IPv6 only.
-n
Print primarily IP addresses numerically.
-b
Print both: Host names and IP addresses.
-l
Sets the initial packet length to pktlen instead of 65535 for
IPv4 or 128000 for IPv6.
-m
Set maximum hops (or maximum TTLs) to max_hops instead of 30.
-p
Sets the initial destination port to use.
-V
Print version and exit.
root@mops:~ # tracepath -6 3ffe:2400:0:109::2
1?: [LOCALHOST] pmtu 1500
1: dust.inr.ac.ru 0.411ms
2: dust.inr.ac.ru asymm 1 0.390ms pmtu 1480
2: 3ffe:2400:0:109::2 463.514ms reached
Resume: pmtu 1480 hops 2 back 2
The first column shows the TTL of the probe, followed by colon.
Usually the value of TTL is obtained from the reply from the
network, but sometimes it does not contain the necessary
information and we have to guess it. In this case the number is
followed by ?.
The second column shows the network hop which replied to the
probe. It is either the address of the router or the word
[LOCALHOST], if the probe was not sent to the network.
The rest of the line shows miscellaneous information about the
path to the corresponding network hop. It contains the value of
RTT, and additionally it can show Path MTU when it changes. If the
path is asymmetric or the probe finishes before it reaches the
prescribed hop, the number of hops in return direction is shown
next to the keyword "asymm". This information is not reliable,
e.g. the third line shows asymmetry of 1. This is because the
first probe with TTL of 2 was rejected at the first hop due to
Path MTU Discovery.
The last line summarizes information about all the paths to the
destination. It shows detected Path MTU, amount of hops to the
destination and our guess about the number of hops from the
destination to us, which can be different when the path is
asymmetric.
In case of errors tracepath prints short error code.
┌─────────────┬──────────────┬────────────────────┐
│ Output │ Code │ Meaning │
├─────────────┼──────────────┼────────────────────┤
│ !A │ EACCES │ Communication │
│ │ │ administratively │
│ │ │ prohibited │
├─────────────┼──────────────┼────────────────────┤
│ !H │ EHOSTUNREACH │ Destination host │
│ │ │ unreachable │
├─────────────┼──────────────┼────────────────────┤
│ !N │ ENETUNREACH │ Destination │
│ │ │ network │
│ │ │ unreachable │
├─────────────┼──────────────┼────────────────────┤
│ !P │ EPROTO │ Destination │
│ │ │ protocol │
│ │ │ unreachable │
├─────────────┼──────────────┼────────────────────┤
│ pmtu N │ EMSGSIZE │ Message too long │
├─────────────┼──────────────┼────────────────────┤
│ reached │ ECONNREFUSED │ Connection refused │
├─────────────┼──────────────┼────────────────────┤
│ │ ETIMEDOUT │ Connection timed │
│ │ │ out │
├─────────────┼──────────────┼────────────────────┤
│ NET ERROR N │ │ Any other error │
└─────────────┴──────────────┴────────────────────┘
traceroute(8), traceroute6(8), ping(8).
tracepath was written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>.
No security issues.
This lapidary deserves to be elaborated. tracepath is not a
privileged program, unlike traceroute, ping and other beasts of
their kind. tracepath may be executed by everyone who has enough
access to the network to send UDP datagrams to the desired
destination using the given port.
tracepath is part of iputils package.
This page is part of the iputils (IP utilities) project.
Information about the project can be found at
⟨http://www.skbuff.net/iputils/⟩. If you have a bug report for
this manual page, send it to yoshfuji@skbuff.net,
netdev@vger.kernel.org. This page was obtained from the project's
upstream Git repository ⟨https://github.com/iputils/iputils.git⟩
on 2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-06-06.) If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a
mail to man-pages@man7.org
iputils 20250605 TRACEPATH(8)
Pages that refer to this page: ip(7), arping(8), clockdiff(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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