tracepath
traces path to a network host discovering MTU along this path
see also :
traceroute6 - ping
Synopsis
tracepath
[-n] [-b] [-l pktlen]
destination [port]
add an example, a script, a trick and tips
examples
no example yet ...
... Feel free to add your own example above to help other Linux-lovers !
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 require superuser
privileges and has no fancy options.
tracepath6
is 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 will be updated. For now it uses
Van Jacobson’s trick, sweeping a range of UDP ports to
maintain trace history.
options
-n
Print primarily IP addresses
numerically.
-b
Print both of host names and IP addresses.
-l
Sets the initial packet length to pktlen instead
of 65536 for tracepath or 128000 for
tracepath6.
availability
tracepath is part of iputils package and the latest
versions are available in source form at
http://www.skbuff.net/iputils/iputils-current.tar.bz2.
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 following 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.
The 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
asymmetric.
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 investigated destination using given port.
see also
traceroute,
traceroute6 , ping .
author
tracepath
was written by Alexey Kuznetsov
<kuznet[:at:]ms2.inr.ac[:dot:]ru>.