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     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.