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TRACEROUTE(8)                                                    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
       increased by specifying a packet length (in bytes) after  the  destina-
       tion 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
              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
              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 - 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
              (default 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
       until  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 gate-
       way  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 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
       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 (got a
       host, network or protocol unreachable, respectively), !S or !F  (source
       route  failed  or  fragmentation  needed - neither of these should ever
       occur and the associated gateway is busted if you see one), !X  (commu-
       nication  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.
       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:


       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
       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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