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

       traceroute - print the route packets take to network host

       traceroute [ -Sdnrv ] [ -g gw_host ] [ -M min_ttl ]
	       [ -m max_ttl ] [	-P proto ] [ -p	port ]
	       [ -q nqueries ] [ -s src_addr ] [ -t tos	]
	       [ -w waittime ] host [ packetlen	]

       The  Internet  is  a large and complex aggregation of network hardware,
       connected together by gateways.	Tracking the route one's packets  fol-
       low  (or	 finding the miscreant gateway that's discarding your packets)
       can be difficult.  Traceroute utilizes the IP protocol `time  to	 live'
       field  and  attempts 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 40 bytes, but this may	be in-
       creased by specifying a packet length (in bytes)	after the  destination
       host name.

       Other options are:

       -S     Print  a	summary	 of how	many probes were not answered for each

       -g     Specify a	loose source route gateway (8 maximum).

       -M     Set the initial time-to-live value used in outgoing probe	 pack-
	      ets.  The	default	is 1, i.e., start with the first hop.

       -m     Set  the	max time-to-live (max number of	hops) used in outgoing
	      probe packets.  The default is net.inet.ip.ttl  hops  (the  same
	      default used for TCP connections).

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

       -P     Send  packets  of	specified IP protocol. The currently supported
	      protocols	are: UDP, TCP and GRE. Other  protocols	 may  also  be
	      specified	 (either by name or by number),	though traceroute does
	      not implement any	special	knowledge  of  their  packet  formats.
	      This  option is useful for determining which router along	a path
	      may be blocking packets based on IP  protocol  number.  But  see
	      BUGS below.

       -p     Protocol	specific.  For	UDP and	TCP, sets the base port	number
	      used in probes (default is 33434).  Traceroute hopes that	 noth-
	      ing  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 something is lis-
	      tening on	a port in the default range, this option can  be  used
	      to pick an unused	port range.

       -q     Set the number of	probes per hop (default	is 3).

       -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
	      network,	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 num-
	      ber, 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
	      (default 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 (de-
	      fault 5 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 un-
       til we get an ICMP "port	unreachable" (which means we got to "host") or
       hit a max (which	defaults to net.inet.ip.ttl 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 dif-
       ferent gateways,	the address of each responding system will be printed.
       If  there is no response	within a 5 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
       destination is using that value,	it can be changed with the -p flag).

       A sample	use and	output might be:

	      [yak 71]%	traceroute
	      traceroute to	(, 64	hops max, 38 byte packet
	       1 (  19 ms  19 ms	 0 ms
	       2  lilac-dmc.Berkeley.EDU (	 39 ms	39 ms  19 ms
	       3  lilac-dmc.Berkeley.EDU (	 39 ms	39 ms  19 ms
	       4  ccngw-ner-cc.Berkeley.EDU (  39	ms  40 ms  39 ms
	       5  ccn-nerif22.Berkeley.EDU (  39 ms  39 ms  39 ms
	       6 (  40 ms  59 ms  59	ms
	       7 (  59	ms  59 ms  59 ms
	       8	(	 99 ms	99 ms  80 ms
	       9 (  139 ms  239 ms  319 ms
	      10 (  220 ms  199 ms  199 ms
	      11	(  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 - - 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

       A more interesting example is:

	      [yak 72]%	traceroute
	      traceroute to (,	64 hops	max
	       1 (  0 ms	 0 ms  0 ms
	       2  lilac-dmc.Berkeley.EDU (	 19 ms	19 ms  19 ms
	       3  lilac-dmc.Berkeley.EDU (	 39 ms	19 ms  19 ms
	       4  ccngw-ner-cc.Berkeley.EDU (  19	ms  39 ms  39 ms
	       5  ccn-nerif22.Berkeley.EDU (  20 ms  39 ms  39 ms
	       6 (  59 ms  119 ms  39 ms
	       7 (  59	ms  59 ms  39 ms
	       8	(	 80 ms	79 ms  99 ms
	       9 (  139 ms  139 ms  159 ms
	      10 (  199 ms  180 ms  300 ms
	      11	(	 300 ms	 239 ms	 239 ms
	      12  * * *
	      13	(	 259 ms	 499 ms	 279 ms
	      14  * * *
	      15  * * *
	      16  * * *
	      17  * * *
	      18  ALLSPICE.LCS.MIT.EDU (  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
       unreachable message using whatever ttl remains in  the  original	 data-
       gram.   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 destina-
       tion system:

	       1 (  0 ms	 0 ms  0 ms
	       2  lilac-dmc.Berkeley.EDU (	 39 ms	19 ms  39 ms
	       3  lilac-dmc.Berkeley.EDU (	 19 ms	39 ms  19 ms
	       4  ccngw-ner-cc.Berkeley.EDU (  39	ms  40 ms  19 ms
	       5  ccn-nerif35.Berkeley.EDU (  39 ms  39 ms  39 ms
	       6  csgw.Berkeley.EDU (  39 ms  59	ms  39 ms
	       7  * * *
	       8  * * *
	       9  * * *
	      10  * * *
	      11  * * *
	      12  * * *
	      13  rip.Berkeley.EDU (  59 ms !  39	ms !  39 ms !

       Notice that there are 12	"gateways" (13 is the final  destination)  and
       exactly	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  ar-
       riving  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) soft-
       ware, 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, or !P	(got a
       host, network or	protocol unreachable, respectively), !S	or !F  (source
       route failed or fragmentation needed - neither of these should ever oc-
       cur and the associated gateway is busted	if you see one), !X  (communi-
       cation administratively prohibited), or !<N> (ICMP unreachable code N).
       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
       management.  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.

       netstat(1), ping(8)

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

       The current version is available	via anonymous ftp:

       When using protocols other than UDP, functionality is reduced.  In par-
       ticular,	 the  last  packet  will often appear to be lost, because even
       though it reaches the destination host, there's no way to know that be-
       cause no	ICMP message is	sent back.  In the TCP case, traceroute	should
       listen for a RST	from the destination host (or an  intermediate	router
       that's filtering	packets), but this is not implemented yet.

       Please send bug reports to

4.3 Berkeley Distribution      27 September 1996		 TRACEROUTE(8)


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