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traceroute(8)

NAME

       traceroute - print the route packets take to network host

SYNOPSIS

       traceroute [ -dFISdnrvx ] [ -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 ]

DESCRIPTION

       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
       increased by specifying a packet length (in bytes) after  the  destina-
       tion host name.

       Other options are:

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

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

       -d     Enable socket level debugging.

       -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
	      icmp").

       -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
	      numerically  (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
	      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 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
	      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. (See the -i flag for another way to do this.)

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

       -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
	      (default 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
	      ICMP.

       -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
       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 nis.nsf.net.
	      traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 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), 64 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.

	       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
       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
       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)  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),  !X  (communication  administratively  prohibited),  !V  (host
       precedence violation), !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.

SEE ALSO

       pathchar(8), netstat(1), ping(8)

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.

       The current version is available via anonymous ftp:

	      ftp://ftp.ee.lbl.gov/traceroute.tar.gz

BUGS

       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
       because	no  ICMP  message  is  sent back.  In the TCP case, traceroute

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