TRACEROUTE linux command manual

TRACEROUTE(8)                                                  TRACEROUTE(8)

       traceroute - print the route packets take to network host

       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 ]

       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  num-
       ber.   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.

       -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

       -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  intermediate  routers, (TOS=!) 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

       -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  set-
       ting 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 differ-
       ent  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 (, 30 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 (, 30 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 ven-
       dors  ship  a  lot of obsolete (DEC's Ultrix, Sun 3.x) or non-standard
       (HPUX) software, 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,
       network or protocol unreachable), !S (source route failed),  !F-
       (fragmentation  needed  - the RFC1191 Path MTU Discovery value is dis-
       played),  (TOS=!)   (TOS  has  been  altered  in  the  path  to
       ),  !X  (communication  administratively  prohibited), !V (host
       precedence violation), !C (precedence cutoff  in  effect),  or  !
       (ICMP  unreachable  code  ).  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:


       Please send bug reports to

4.3 Berkeley Distribution     21 September 2000                 TRACEROUTE(8)