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TRACEROUTE(8)                                                    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
       increased by specifying a packet length (in bytes) after  the  destina-
       tion 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
              underscores.  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
              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 * 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
              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

       -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

       -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
       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  - 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
       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), !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
       unreachable), !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.
       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      21 September 2000                 TRACEROUTE(8)


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