Provided by: iputils-tracepath_20121221-5ubuntu2_amd64 bug


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


       tracepath [-n] [-b] [-l pktlen] [-m max_hops] [-p port] destination


       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.


       -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 65535 for tracepath or 128000
              for tracepath6.

              Set maximum hops (or maximum TTLs) to max_hops instead of 30.

       -p     Sets the initial destination port to use.


       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 network
       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.


       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 port.


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