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NetBSD 6.1.5 - man page for traceroute (netbsd section 8)


       traceroute - print the route packets take to network host

       traceroute [ -aDFPIdlMnrvx ] [ -f first_ttl ]
	       [ -g gateway ] [ -i iface ] [ -m max_ttl ]
	       [ -p port ] [ -q nqueries ] [ -s src_addr ]
	       [ -t tos ] [ -w waittime ] [ -z pausemsecs
	] ] [ -A as_server ]
	       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 uses 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 40 bytes, but this may be increased by specifying a packet  length  (in
       bytes) after the destination host name.

       Other options are:

       -a     Turn on AS# lookups for each hop encountered.

       -A     Turn on AS# lookups and use the given server instead of the default.

       -d     Turn on socket-level debugging.

       -D     Dump the packet data to standard error before transmitting it.

       -f     Set the initial time-to-live used in the first outgoing probe packet.

       -F     Set the "don't fragment" bit.

       -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.

       -l     Display  the  ttl  value	of  the returned packet.  This is useful for checking for
	      asymmetric routing.

       -m     Set the max time-to-live (max number of hops) used in outgoing probe packets.   The
	      default value is taken from the net.inet.ip.ttl sysctl(3) variable.

       -M     If found, show the MPLS Label and the Experimental (EXP) bit for the hop.

       -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.

       -P     Set the "don't fragment" bit, and use the next hop mtu each time we get  the  "need
	      fragmentation" error, thus probing the path MTU.

       -q     Set  the	number	of probe packets sent for each hop.  By default, traceroute sends
	      three probe packets.

       -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(8)).

       -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 calculated). 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 -
       lilac-dmc.Berkeley.EDU - 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 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 (HP-UX) 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  !N  (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.

	      traceroute -g

       will show the path from the Cambridge Mailbridge to PSC, while

	      traceroute -g -g

       will show the path from the Cambridge Mailbridge to Merit, using PSC to	reach  the  Mail-

       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

       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.

       The AS number capability reports information that may sometimes be inaccurate due to  dis-
       crepancies  between  the  contents of the routing database server and the current state of
       the Internet.

4.3 Berkeley Distribution		21 September 2000			    TRACEROUTE(8)

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