Provided by: iputils-tracepath_20020927-3ubuntu1_i386 bug


       tracepath,  tracepath6  - traces path to a network host discovering MTU
       along this path


       tracepath destination [ port]


       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.


       root@mops:~ # tracepath6 3ffe:2400:0:109::2
        1?: [LOCALHOST]                              pmtu 1500
        1:                   0.411ms
        2:        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 asymmetric.


       traceroute(8), traceroute6(8), ping(8).


       tracepath was written by Alexey Kuznetsov <>.


       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


       tracepath is part of  iputils  package  and  the  latest  versions  are
       available  in  source  form  from anonymous ftp