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 [ -n]  [ -b]  [ -l pktlen]  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  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 65536 for tracepath or 128000 for tracepath6.

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 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.

       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 <kuznetATms2.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-100418                                            13 July 2010                                              TRACEPATH(8)