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

       traceroute - print the route packets take to network host

       traceroute [ -dDeFISnrvx	] [ -f first_ttl ] [ -g	gateway	]
	       [ -i iface ] [ -M first_ttl ]
	       [ -m max_ttl ] [	-P proto ] [ -p	port ]
	       [ -q nqueries ] [ -s src_addr ] [ -t tos	]
	       [ -w waittime ] [ -z pausemsecs ]
	       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:

       -e     Firewall	evasion	mode.  Use fixed destination ports for UDP and
	      TCP probes.  The destination port	does NOT increment  with  each
	      packet sent.

       -f     Set  the	initial	 time-to-live used in the first	outgoing probe

       -F     Set the "don't fragment" bit.

       -d     Enable socket level debugging.

       -D     When an ICMP response to our probe datagram is  received,	 print
	      the  differences	between	 the transmitted packet	and the	packet
	      quoted by	the ICMP response.  A  key  showing  the  location  of
	      fields within the	transmitted packet is printed, followed	by the
	      original packet in hex, followed by the quoted  packet  in  hex.
	      Bytes  that  are unchanged in the	quoted packet are shown	as un-
	      derscores.  Note,	the IP checksum	and  the  TTL  of  the	quoted
	      packet  are  not	expected to match.  By default,	only one probe
	      per hop is sent with this	option.

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

       -i     Specify a	network	interface to obtain the	source IP address  for
	      outgoing probe packets. This is normally only useful on a	multi-
	      homed host. (See the -s flag for another way to do this.)

       -I     Use ICMP ECHO instead of UDP  datagrams.	 (A  synonym  for  "-P

       -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,	GRE and	ICMP. Other protocols may also
	      be specified (either by name or by  number),  though  traceroute
	      does  not	 implement  any	special	knowledge of their packet for-
	      mats. 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 * nprobes - 1
	      at  the  destination  host  (so an ICMP PORT_UNREACHABLE message
	      will be returned to terminate the	route tracing).	 If  something
	      is  listening 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,	unless	-D  is
	      specified, when it is 1).

       -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 usually is	given as an IP
	      number, not a hostname) as the source address in outgoing	 probe
	      packets.	 On multi-homed	hosts (those with more than one	IP ad-
	      dress), 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. (See the	-i flag	for another way	to do this.)

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

       -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.).

       -x     Toggle  ip  checksums.  Normally,	 this prevents traceroute from
	      calculating ip checksums.	In some	cases,	the  operating	system
	      can  overwrite  parts of the outgoing packet but not recalculate
	      the checksum (so in some cases the default is to	not  calculate
	      checksums	 and using -x causes them to be	calculated). Note that
	      checksums	are usually required for the last hop when using  ICMP
	      ECHO  probes  (-I).   So	they  are always calculated when using

       -z     Set the time (in milliseconds) to	pause between probes  (default
	      0).   Some  systems  such	 as Solaris and	routers	such as	Ciscos
	      rate limit icmp messages.	A good value to	use with this this  is
	      500 (e.g.	1/2 second).

       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  -	lilac-dmc.Berkeley.EDU - 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
	      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 (host, net-
       work or protocol	unreachable),  !S  (source  route  failed),  !F-<pmtu>
       (fragmentation  needed  -  the RFC1191 Path MTU Discovery value is dis-
       played),	!U or !W (destination network/host unknown), !I	 (source  host
       is  isolated),  !A  (communication with destination network administra-
       tively prohibited), !Z (communication with destination host administra-
       tively  prohibited),  !Q	 (for  this ToS	the destination	network	is un-
       reachable), !T (for this	ToS the	destination host is  unreachable),  !X
       (communication administratively prohibited), !V (host precedence	viola-
       tion), !C (precedence cutoff in effect),	or  !<num>  (ICMP  unreachable
       code  <num>).  These are	defined	by RFC1812 (which supersedes RFC1716).
       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.

       pathchar(8), 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      21 September 2000		 TRACEROUTE(8)


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