*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->OpenBSD man pages -> traceroute (8)              



NAME    [Toc]    [Back]

     traceroute - print the route packets take to network host

SYNOPSIS    [Toc]    [Back]

     traceroute [-cdDIlnrSv] [-f first_ttl] [-g gateway_addr] [-m
                [-p  port] [-P proto] [-q nqueries] [-s src_addr]
[-t tos]
                [-w waittime] host [packetsize]

DESCRIPTION    [Toc]    [Back]

     The Internet is a large and complex aggregation  of  network
hardware, connected
 together by gateways.  Tracking the route one's packets follow (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 38 bytes, but this  may
be increased
     by specifying a packet size (in bytes) after the destination
host name.

     The options are as follows:

     -c      Do not increment the destination port number in successive UDP
             packets.  Rather, all UDP packets will have the same
             port, as set via the -p flag (or 33434  if  none  is

     -d      Turn on socket-level debugging.

     -D      Dump the packet data to standard error before transmitting it.

     -f first_ttl
             Set the first time-to-live used  in  outgoing  probe
packets. The
             effect is that the first first_ttl - 1 hosts will be
skipped in
             the output of traceroute.  The default  value  is  1
(skip no

     -g gateway_addr
             Add  gateway_addr to the list of addresses in the IP
Loose Source
             Record Route (LSRR)  option.   If  no  gateways  are
specified, the
             LSRR option is omitted.

     -I       Equivalent  to  -P  1.  Used for compatibility with
other OSes.

     -l      Display the ttl value of the returned packet.   This
is useful for
             checking for asymmetric routing.

     -m max_ttl
             Set  the  max time-to-live (max number of hops) used
in outgoing
             probe packets.  The default is the value of the system's
             net.inet.ip.ttl  MIB variable, which defaults to 64.

     -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 port
             Set the base UDP port number used in probes (default
is 33434).
             traceroute  hopes  that  nothing is listening on UDP
ports base to
             base+nhops*nqueries-1 at the destination host (so an
             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.

     -P proto
             Change the protocol being used from UDP to a numeric
protocol or
             a  name  as  specified in /etc/protocols.  This will
not work reliably
 for most protocols.  If set to 1  (ICMP),  then
ICMP Echo Request
 messages will be used (same as ping(8)).

     -q nqueries
             Set  the  number  of  probes per ``ttl'' to nqueries
(default is
             three probes).

     -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(8)).

     -s src_addr
             Use the following IP address (which must be given as
an IP number,
 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
             and  the  user is not the superuser, an error is returned and nothing
 is sent.

     -S      Print how many probes were  not  answered  for  each

     -t tos  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-ofservice
 result in different paths.  (If you are  not
running a
             4.3BSD-Tahoe  or  later system, 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
             and UNREACHABLEs are listed.

     -w waittime
             Set the time (in seconds) to wait for a response  to
a probe (default

     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 out 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 64 hops and can be changed  with  the  -m
flag).  Three
     probes  (changed  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 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:

           $ traceroute nis.nsf.net.
           traceroute to nis.nsf.net (, 64 hops max, 56
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
           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 4.3 BSD).  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:

           $ 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
           11 (  300 ms  239 ms  239
           12  * * *
           13 (  259 ms  499 ms  279
           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
     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 destination

           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 (HP-UX) software, expect to
see this
     problem frequently and/or take care picking the target  host
of your

     Other  possible  annotations  after  the time are !H, !N, !P
(got a host,
     network or protocol unreachable, respectively), !A, !C  (access to the
     network  or host, respectively, is prohibited), !X (communication administratively
 prohibited by filtering), !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), !U (destination network or host
     unknown),  !T  (destination  network or host unreachable for
TOS), !<code>
     (other ICMP unreachable code).  If almost all the probes result in some
     kind of unreachable, traceroute will give up and exit.

           $ traceroute -g

     will  show  the  path  from the Cambridge Mailbridge to PSC,

           $ traceroute -g -g

     will show the path from the Cambridge Mailbridge  to  Merit,
using PSC to
     reach the Mailbridge.

     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

SEE ALSO    [Toc]    [Back]

     netstat(1), ping(8)

HISTORY    [Toc]    [Back]

     The   very  first  traceroute  (never  released)  used  ICMP
ECHO_REQUEST datagrams
 as probe packets.  During the first night  of  testing
it was discovered
  that  more  than  half  the router vendors of the time
would not return
     an ICMP TIME_EXCEEDED for an ECHO_REQUEST.   traceroute  was
then changed
     to  use  UDP  probe packets.  Most modern TCP/IP implementations will now
     generate an ICMP error message to ICMP query  messages,  and
the option to
     use ECHO_REQUEST probes was re-implemented.

     The traceroute command first appeared in 4.4BSD.

AUTHORS    [Toc]    [Back]

     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.

OpenBSD      3.6                           June      6,      1993
[ Back ]
 Similar pages
Name OS Title
traceroute IRIX print the route packets take to a network host
traceroute Tru64 Prints the route that packets take to a network host
traceroute6 FreeBSD print the route IPv6 packets will take to the destination
traceroute6 OpenBSD print the route IPv6 packets will take to the destination
ping HP-UX send ICMP Echo Request packets to network host
nsip OpenBSD software network interface encapsulating NS packets in IP packets
spray OpenBSD send many packets to host
spray FreeBSD send many packets to host
ipresend FreeBSD resend IP packets out to network
snoop IRIX capture and inspect network packets
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service