Switch to SpeakEasy.net DSL

The Modular Manual Browser

Home Page
Manual: (FreeBSD-5.4-RELEASE)
Apropos / Subsearch:
optional field

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

       traceroute - print the route packets take to network host

       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 ]

       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

       -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

       -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 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 nis.nsf.net.
              traceroute to nis.nsf.net (, 64 hops max, 38 byte packet
               1  helios.ee.lbl.gov (  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  nic.merit.edu (  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

       A more interesting example is:

              [yak 72]% traceroute allspice.lcs.mit.edu.
              traceroute to allspice.lcs.mit.edu (, 64 hops max
               1  helios.ee.lbl.gov (  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  helios.ee.lbl.gov (  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-<&lt;pmtu>&gt;
       (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  !<&lt;num>&gt;
       (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 tracerouteATee.gov.

4.3 Berkeley Distribution      21 September 2000                 TRACEROUTE(8)