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OpenDarwin 7.2.1 - man page for traceroute (opendarwin section 8)

TRACEROUTE(8)			   BSD System Manager'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 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.  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.

     Other options are:

     -m max_ttl
	     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 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-1 at the destination host
	     (so an ICMP PORT_UNREACHABLE message will be returned to terminate the route trac-
	     ing).  If something is listening on a port in the default range, this option can be
	     used to pick an unused port range.

     -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, an error is returned and nothing
	     is sent.

     -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-of-service result in different paths.  (If you are not run-
	     ning 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 proba-
	     bly '-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 (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 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
     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
     4.3 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:

     [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 Gate-
     way 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 (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) 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, !P (got a host, network or protocol unreachable,
     respectively), !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).  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.

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

SEE ALSO
     netstat(1), ping(8)

HISTORY
     The traceroute command is currently in beta test.

4.3 Berkeley Distribution		   June 1, 1994 		4.3 Berkeley Distribution


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