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 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	tracepath  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.

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.	Addi-
       tionally, it can show Path MTU, when it changes.	 If the path is asym-
       metric or the probe finishes before it reach prescribed	hop,  differ-
       ence 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.

       Te 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 .

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 from  anonymous	 ftp  ftp://ftp.inr.ac.ru/ip-
       routing/iputils-current.tar.gz.



iputils-020927		      27 September 2002			 TRACEPATH(8)

UNIX/Linux commands referenced on this page:

1. host
2. column
3. which
4. at
5. last
6. traceroute
7. ping
8. who
9. ftp