TRACEROUTE(8)						      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 ] [ -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 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 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 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 net-
	      work,  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 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 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 through-
	      put).

       -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
	       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  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, !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 thousands with particularly cogent suggestions or
       fixes from C. Philip Wood, Tim Seaver and Ken Adelman.

SEE ALSO

       netstat(1), ping(8)

4.3 Berkeley Distribution					 February 28, 1989						     TRACEROUTE(8)