# 2.11BSD#431 - /usr/man/cat8/traceroute.0

    TRACEROUTE(8)	    UNIX Programmer's Manual	    TRACEROUTE(8)

    NAME
         traceroute - print the route packets take to network host

    SYNOPSIS
         traceroute [ -m max_ttl ] [ -n ] [ -p port ] [ -q nqueries ]
         [ -r ] [ -s src_addr ] [ -t tos ] [ -w ] [ -w waittime ]
         host [ packetsize ]

    DESCRIPTION
         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.	Tra-
         ceroute 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.

         Other options are:

         -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 symboli-
    	  cally 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 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

    Printed 11/26/99	February 28, 1989			1

    TRACEROUTE(8)	    UNIX Programmer's Manual	    TRACEROUTE(8)

    	  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.

         -t   Set the type-of-service in probe packets to the follow-
    	  ing 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 dif-
    	  ferent paths.  (If you are not running 4.4bsd, this may
    	  be academic since the normal network services like tel-
    	  net 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 3 sec.).

         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 3 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, 56 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

    Printed 11/26/99	February 28, 1989			2

    TRACEROUTE(8)	    UNIX Programmer's Manual	    TRACEROUTE(8)

    	   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 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 des-
         tination 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

    Printed 11/26/99	February 28, 1989			3

    TRACEROUTE(8)	    UNIX Programmer's Manual	    TRACEROUTE(8)

    	   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 desti-
         nation) 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) software,
         expect to see this problem frequently and/or take care pick-
         ing the target host of your probes.

         Other possible annotations after the time are !H, !N, !P
         (got a host, network or protocol unreachable, respectively),
         !S or !F (source route failed or fragmentation needed - nei-
         ther of these should ever occur and the associated gateway
         is busted if you see one).  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, meas-
         urement 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.

    AUTHOR
         Implemented by Van Jacobson from a suggestion by Steve Deer-
         ing.  Debugged by a cast of thousands with particularly
         cogent suggestions or fixes from C. Philip Wood, Tim Seaver
         and Ken Adelman.

    SEE ALSO
         netstat(1), ping(8)

    Printed 11/26/99	February 28, 1989			4

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