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 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.	 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 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-cur-
       rent.tar.bz2.

iputils-101006							   12 April 2011						      TRACEPATH(8)