NAME

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

SYNOPSIS

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

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 65535 for tracepath or 128000 for tracepath6.

       -m/term>
              Set maximum hops (or maximum TTLs) to max_hops instead of 30.

       -p     Sets the initial destination port to use.

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 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.

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  at
       http://www.skbuff.net/iputils/iputils-current.tar.bz2.

iputils-121221                                     07 May 2014                                      TRACEPATH(8)