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TRACEPATH(8) System Manager's Manual: iputils TRACEPATH(8)
NAME
tracepath, tracepath6 - traces path to a network host discovering MTU along this
path
SYNOPSIS
tracepath [-nc] <destination>[/<port>]
DESCRIPTION
It traces path to destination discovering MTU along this path. It uses UDP port
port or some random port. It is similar to traceroute, only does not not require
superuser privileges. Option -c causes tracepath to use the return address instead
of the reply type (connection refused) to determine when to stop.
tracepath6 is good replacement for traceroute6 and classic example of application
of Linux error queues. The situation with tracepath is worse, because commercial
IP routers do not return enough information in icmp error messages. Probably, it
will change, when they will be updated. For now it uses Van Jacobson's trick,
sweeping a range of UDP ports to maintain trace history.
OUTPUT
root@mops:~ # tracepath6 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 TTL of the probe, followed by colon. Usually value of TTL
is obtained from reply from network, but sometimes reply does not contain 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
address of router or word [LOCALHOST], if the probe was not sent to the network.
The rest of line shows miscellaneous information about path to the correspinding
hetwork hop. As rule it contains value of RTT. Additionally, it can show Path MTU,
when it changes. If the path is asymmetric or the probe finishes before it reach
prescribed hop, difference between number of hops in forward and backward direction
is shown folloing keyword async. This information is not reliable. F.e. the third
line shows asymmetry of 1, it is because the first probe with TTL of 2 was rejected
at the first hop due to Path MTU Discovery.
Te last line summarizes information about all the path to the destination, it shows
detected Path MTU, amount of hops to the destination and our guess about amount of
hops from the destination to us, which can be different when the path is asymmet-
ric.
SEE ALSO
traceroute(8), traceroute6(8), ping(8).
AUTHOR
tracepath was written by Alexey Kuznetsov <kuznet AT ms2.ru>.
SECURITY
No security issues.
This lapidary deserves to be elaborated. tracepath is not a privileged program,
unlike traceroute, ping and other beasts of this kind. tracepath may be executed
by everyone who has some access to network, enough to send UDP datagrams to inves-
tigated destination using given port.
AVAILABILITY
tracepath is part of iputils package and the latest versions are available in
source form from anonymous ftp ftp://ftp.inr.ac.ru/ip-routing/iputils-cur-
rent.tar.gz.
iputils-020927 27 September 2002 TRACEPATH(8)
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On Apache/1.3.37 (Unix) mod_throttle/3.1.2 FrontPage/5.0.2.2635 mod_psoft_traffic/0.2 mod_ssl/2.8.28 OpenSSL/0.9.8b
Under GNU General Public License
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