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] [-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.

       -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 cor-
       respinding network hop. As rule it contains value  of  RTT.   Addition-
       ally, 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 fol-
       lowing 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 destina-
       tion, 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.	  tra-
       cepath  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-cur-
       rent.tar.bz2.



iputils-121221			  17 May 2016			  TRACEPATH(8)