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RedHat 9 (Linux i386) - man page for traceroute (redhat section 8)

TRACEROUTE(8)			     System Manager's Manual			    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  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 gate-
       way 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 destination 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 net-
	      work.  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  host-
	      name) 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 mean-
	      ingful - 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  check-
	      sums.  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

       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 (, 30 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 NSSes.

       A more interesting example is:

	      [yak 72]% traceroute allspice.lcs.mit.edu.
	      traceroute to allspice.lcs.mit.edu (, 30 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 datagram.  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 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 prob-
       lem 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) 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-<pmtu> (fragmentation needed - the RFC1191 Path
       MTU Discovery value is displayed),  !X  (communication  administratively  prohibited),  !V
       (host precedence violation), !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

       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 traceroute@ee.lbl.gov.

4.3 Berkeley Distribution		21 September 2000			    TRACEROUTE(8)

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