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TRACEROUTE(8)		     System Manager's Manual		   TRACEROUTE(8)

NAME
     traceroute - print the route packets take to network host

SYNOPSIS
     traceroute  [  -m	max_ttl ] [ -n ] [ -p port ] [ -q nqueries ] [ -r ] [ -s
     src_addr ] [ -t tos ] [ -w ] [ -w waittime ] host [ packetsize ]

DESCRIPTION
     The Internet is a large and complex aggregation of network  hardware,  con-
     nected  together  by gateways.  Tracking the route one's packets follow (or
     finding the miscreant gateway that's discarding your packets) can be diffi-
     cult.  Traceroute utilizes the IP protocol `time to  live'  field	and  at-
     tempts to elicit an ICMP TIME_EXCEEDED response from each gateway along the
     path to some host.

     The  only	mandatory  parameter  is the destination host name or IP number.
     The default probe datagram length is 38 bytes, but this may be increased by
     specifying a packet size (in bytes) after the destination host name.

     Other options are:

     -m     Set the max time-to-live (max number of hops) used in outgoing probe
	    packets.  The default is 30 hops (the same default used for TCP con-
	    nections).

     -n     Print hop addresses numerically rather than symbolically and numeri-
	    cally (saves a nameserver address-to-name lookup  for  each  gateway
	    found on the path).

     -p     Set  the  base  UDP  port  number used in probes (default is 33434).
	    Traceroute hopes that nothing is listening	on  UDP  ports	base  to
	    base+nhops-1  at  the  destination host (so an ICMP PORT_UNREACHABLE
	    message will be returned to terminate the route tracing).  If  some-
	    thing  is  listening on a port in the default range, this option can
	    be used to pick an unused port range.

     -r     Bypass the normal routing tables and send directly to a host  on  an
	    attached  network.	 If  the host is not on a directly-attached net-
	    work, an error is returned.  This option can be used to ping a local
	    host through an interface that has no route through it (e.g.,  after
	    the interface was dropped by routed(8C)).

     -s     Use  the  following IP address (which must be given as an IP number,
	    not a hostname) as the source address in outgoing probe packets.  On
	    hosts with more than one IP address, this  option  can  be	used  to
	    force  the	source address to be something other than the IP address
	    of the interface the probe packet is sent on.  If the IP address  is
	    not  one of this machine's interface addresses, an error is returned
	    and nothing is sent.

     -t     Set the type-of-service in probe packets to the following value (de-
	    fault zero).  The value must be a decimal integer in the range 0  to
	    255.   This  option can be used to see if different types-of-service
	    result in different paths.	(If you are not running 4.4bsd, this may
	    be academic since the normal network services like	telnet	and  ftp
	    don't  let you control the TOS).  Not all values of TOS are legal or
	    meaningful - see the IP spec for  definitions.   Useful  values  are
	    probably `-t 16' (low delay) and `-t 8' (high throughput).

     -v     Verbose  output.  Received ICMP packets other than TIME_EXCEEDED and
	    UNREACHABLEs are listed.

     -w     Set the time (in seconds) to wait for a response to a probe (default
	    3 sec.).

     This program attempts to trace the route an IP packet would follow to  some
     internet  host  by  launching  UDP  probe packets with a small ttl (time to
     live) then listening for an ICMP "time exceeded" reply from a gateway.   We
     start our probes with a ttl of one and increase by one until we get an ICMP
     "port  unreachable"  (which means we got to "host") or hit a max (which de-
     faults to 30 hops & can be changed with the -m flag).  Three probes (change
     with -q flag) are sent at each ttl setting and a line  is	printed  showing
     the  ttl, address of the gateway and round trip time of each probe.  If the
     probe answers come from different gateways, the address of each  responding
     system  will  be  printed.  If there is no response within a 3 sec. timeout
     interval (changed with the -w flag), a "*" is printed for that probe.

     We don't want the destination host to process the UDP probe packets so  the
     destination  port is set to an unlikely value (if some clod on the destina-
     tion is using that value, it can be changed with the -p flag).

     A sample use and output might be:

	    [yak 71]% traceroute nis.nsf.net.
	    traceroute to nis.nsf.net (35.1.1.48), 30 hops max, 56 byte packet
	     1	helios.ee.lbl.gov (128.3.112.1)  19 ms	19 ms  0 ms
	     2	lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  39 ms  19 ms
	     3	lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  39 ms  19 ms
	     4	ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  39 ms  40 ms  39 ms
	     5	ccn-nerif22.Berkeley.EDU (128.32.168.22)  39 ms  39 ms	39 ms
	     6	128.32.197.4 (128.32.197.4)  40 ms  59 ms  59 ms
	     7	131.119.2.5 (131.119.2.5)  59 ms  59 ms  59 ms
	     8	129.140.70.13 (129.140.70.13)  99 ms  99 ms  80 ms
	     9	129.140.71.6 (129.140.71.6)  139 ms  239 ms  319 ms
	    10	129.140.81.7 (129.140.81.7)  220 ms  199 ms  199 ms
	    11	nic.merit.edu (35.1.1.48)  239 ms  239 ms  239 ms

     Note that lines 2 & 3 are the same.  This is due to a buggy kernel  on  the
     2nd  hop  system - lbl-csam.arpa - that forwards packets with a zero ttl (a
     bug in the distributed version of 4.3BSD).  Note that  you  have  to  guess
     what  path  the packets are taking cross-country since the NSFNet (129.140)
     doesn't supply address-to-name translations for its NSSes.

     A more interesting example is:

	    [yak 72]% traceroute allspice.lcs.mit.edu.
	    traceroute to allspice.lcs.mit.edu (18.26.0.115), 30 hops max
	     1	helios.ee.lbl.gov (128.3.112.1)  0 ms  0 ms  0 ms
	     2	lilac-dmc.Berkeley.EDU (128.32.216.1)  19 ms  19 ms  19 ms
	     3	lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  19 ms  19 ms
	     4	ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  19 ms  39 ms  39 ms
	     5	ccn-nerif22.Berkeley.EDU (128.32.168.22)  20 ms  39 ms	39 ms
	     6	128.32.197.4 (128.32.197.4)  59 ms  119 ms  39 ms
	     7	131.119.2.5 (131.119.2.5)  59 ms  59 ms  39 ms
	     8	129.140.70.13 (129.140.70.13)  80 ms  79 ms  99 ms
	     9	129.140.71.6 (129.140.71.6)  139 ms  139 ms  159 ms
	    10	129.140.81.7 (129.140.81.7)  199 ms  180 ms  300 ms
	    11	129.140.72.17 (129.140.72.17)  300 ms  239 ms  239 ms
	    12	* * *
	    13	128.121.54.72 (128.121.54.72)  259 ms  499 ms  279 ms
	    14	* * *
	    15	* * *
	    16	* * *
	    17	* * *
	    18	ALLSPICE.LCS.MIT.EDU (18.26.0.115)  339 ms  279 ms  279 ms

     Note that the gateways 12, 14, 15, 16 & 17 hops away either don't send ICMP
     "time exceeded" messages or send them with a ttl too small to reach us.  14
     - 17 are running the MIT C Gateway code that doesn't send "time exceeded"s.
     God only knows what's going on with 12.

     The silent gateway 12 in the above may be	the  result  of  a  bug  in  the
     4.[23]BSD	network  code  (and its derivatives):  4.x (x <= 3) sends an un-
     reachable message using whatever ttl  remains  in	the  original  datagram.
     Since, for gateways, the remaining ttl is zero, the ICMP "time exceeded" is
     guaranteed to not make it back to us.  The behavior of this bug is slightly
     more interesting when it appears on the destination system:

	     1	helios.ee.lbl.gov (128.3.112.1)  0 ms  0 ms  0 ms
	     2	lilac-dmc.Berkeley.EDU (128.32.216.1)  39 ms  19 ms  39 ms
	     3	lilac-dmc.Berkeley.EDU (128.32.216.1)  19 ms  39 ms  19 ms
	     4	ccngw-ner-cc.Berkeley.EDU (128.32.136.23)  39 ms  40 ms  19 ms
	     5	ccn-nerif35.Berkeley.EDU (128.32.168.35)  39 ms  39 ms	39 ms
	     6	csgw.Berkeley.EDU (128.32.133.254)  39 ms  59 ms  39 ms
	     7	* * *
	     8	* * *
	     9	* * *
	    10	* * *
	    11	* * *
	    12	* * *
	    13	rip.Berkeley.EDU (128.32.131.22)  59 ms !  39 ms !  39 ms !

     Notice  that  there are 12 "gateways" (13 is the final destination) and ex-
     actly the last half of them are "missing".  What's really happening is that
     rip (a Sun-3 running Sun OS3.5) is using the ttl from our arriving datagram
     as the ttl in its ICMP reply.  So, the reply will time out  on  the  return
     path  (with  no  notice sent to anyone since ICMP's aren't sent for ICMP's)
     until we probe with a ttl that's at least twice the path length.  I.e., rip
     is really only 7 hops away.  A reply that returns with a ttl of 1 is a clue
     this problem exists.  Traceroute prints a "!" after the time if the ttl  is
     <= 1.  Since vendors ship a lot of obsolete (DEC's Ultrix, Sun 3.x) or non-
     standard (HPUX) software, expect to see this problem frequently and/or take
     care picking the target host of your probes.

     Other  possible annotations after the time are !H, !N, !P (got a host, net-
     work or protocol unreachable, respectively), !S or !F (source route  failed
     or  fragmentation needed - neither of these should ever occur and the asso-
     ciated gateway is busted if you see one).	If almost all the probes  result
     in some kind of unreachable, traceroute will give up and exit.

     This  program  is intended for use in network testing, measurement and man-
     agement.  It should be used primarily for manual fault isolation.	 Because
     of  the load it could impose on the network, it is unwise to use traceroute
     during normal operations or from automated scripts.

AUTHOR
     Implemented by Van Jacobson from a suggestion by Steve  Deering.	Debugged
     by  a  cast of thousands with particularly cogent suggestions or fixes from
     C. Philip Wood, Tim Seaver and Ken Adelman.

SEE ALSO
     netstat(1), ping(8)

4.3 Berkeley Distribution	  June 24, 1990 		   TRACEROUTE(8)
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