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 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 and has no fancy options.

       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 cor-
       respinding  hetwork  hop.  As rule it contains value of RTT.  Addition-
       ally, 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  fol-
       loing  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 destina-
       tion, 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.

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  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.

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-current.tar.gz.



iputils-020927                 27 September 2002                  TRACEPATH(8)