TRACEPATH(8) iputils TRACEPATH(8)
NAME
tracepath - traces path to a network host discovering MTU along this
path
SYNOPSIS
tracepath [-4] [-6] [-n] [-b] [-l pktlen] [-m max_hops] [-p port] [-V]
{destination}
DESCRIPTION
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.
OPTIONS
-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.
OUTPUT
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 difference between number of hops in forward and return direction
is shown next to the keyword "async". 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.
SEE ALSO
traceroute(8), traceroute6(8), ping(8).
AUTHOR
tracepath was written by Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>.
SECURITY
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.
AVAILABILITY
tracepath is part of iputils package.
iputils 20221126 TRACEPATH(8)
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