traceroute



TRACEROUTE(8)                                                    TRACEROUTE(8)




NAME

       traceroute - print the route packets take to network host


SYNOPSIS

       traceroute [ -dFInrvx ] [ -f first_ttl ] [ -g gateway ]
               [ -i iface ] [ -m max_ttl ] [ -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.

       -m     Set the max time-to-live (max number of hops) used  in  outgoing
              probe  packets.   The  default is 30 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     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  -  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.

       -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.)

       -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).  If TOS value is changed by inter-
              mediate  routers,  (TOS=<value>!) will be printed once: value is
              the decimal value of the changed TOS byte.

       -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 calcualted). 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
       (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 30 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 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:

              [yak 71]% traceroute nis.nsf.net.
              traceroute to nis.nsf.net (35.1.1.48), 30 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), 30 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.

       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 (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), (TOS=<value>!)  (TOS has been altered in the path to <value>),
       !X (communication administratively  prohibited),  !V  (host  precedence
       violation),  !C (precedence cutoff in effect), or !<num> (ICMP unreach-
       able 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

       Please send bug reports to traceroute@ee.lbl.gov.



4.3 Berkeley Distribution      21 September 2000                 TRACEROUTE(8)

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