traceroute man page on FreeBSD

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       traceroute - print the route packets take to network host

       traceroute [ -adDeFISnrvx ] [ -f first_ttl ] [ -g gateway ]
	       [ -i iface ] [ -M first_ttl ]
	       [ -m max_ttl ] [ -P proto ] [ -p port ]
	       [ -q nqueries ] [ -s src_addr ] [ -t tos ]
	       [ -w waittime ] [ -A as_server ] [ -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  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  40  bytes,  but  this may be
       increased by specifying a packet length (in bytes) after	 the  destina‐
       tion 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

       -e     Firewall evasion mode.  Use fixed destination ports for UDP  and
	      TCP  probes.   The destination port does NOT increment with each
	      packet sent.

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

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

       -d     Enable socket level debugging.

       -D     When  an	ICMP response to our probe datagram is received, print
	      the differences between the transmitted packet  and  the	packet
	      quoted  by  the  ICMP  response.	 A key showing the location of
	      fields within the transmitted packet is printed, followed by the
	      original	packet	in  hex, followed by the quoted packet in hex.
	      Bytes that are unchanged in  the	quoted	packet	are  shown  as
	      underscores.   Note,  the	 IP checksum and the TTL of the quoted
	      packet are not expected to match.	 By default,  only  one	 probe
	      per hop is sent with this option.

       -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.  (A synonym for "-P

       -M     Set the initial time-to-live value used in outgoing probe	 pack‐
	      ets.  The default is 1, i.e., start with the first hop.

       -m     Set  the	max time-to-live (max number of hops) used in outgoing
	      probe packets.  The default is net.inet.ip.ttl  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     Send  packets  of specified IP protocol. The currently supported
	      protocols are: UDP, TCP, GRE and ICMP. Other protocols may  also
	      be  specified  (either  by name or by number), though traceroute
	      does not implement any special knowledge of  their  packet  for‐
	      mats. This option is useful for determining which router along a
	      path may be blocking packets based on IP	protocol  number.  But
	      see BUGS below.

       -p     Protocol	specific.  For	UDP and TCP, sets the base port number
	      used in probes (default is 33434).  Traceroute hopes that	 noth‐
	      ing is listening on UDP ports base to base + nhops * nprobes - 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.

       -q     Set  the	number	of  probes per hop (default is 3, unless -D is
	      specified, when it is 1).

       -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 usually is given  as	an  IP
	      number,  not a hostname) 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.)

       -S     Print  a	summary	 of how many probes were not answered for each

       -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 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  checksums.  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

       -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 net.inet.ip.ttl 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 gate‐
       way 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 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
	      traceroute to (, 64 hops max, 38 byte packet
	       1 (  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 (  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 NSSes.

       A more interesting example is:

	      [yak 72]% traceroute
	      traceroute to (, 64 hops max
	       1 (  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 data‐
       gram.  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 (  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	 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, or !P (host, net‐
       work  or	 protocol  unreachable),  !S  (source route failed), !F-<pmtu>
       (fragmentation needed - the RFC1191 Path MTU Discovery  value  is  dis‐
       played),	 !U  or !W (destination network/host unknown), !I (source host
       is isolated), !A (communication with  destination  network  administra‐
       tively prohibited), !Z (communication with destination host administra‐
       tively prohibited),  !Q	(for  this  ToS	 the  destination  network  is
       unreachable), !T (for this ToS the destination host is unreachable), !X
       (communication administratively prohibited), !V (host precedence viola‐
       tion),  !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 scripts.

       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:

       When using protocols other than UDP, functionality is reduced.  In par‐
       ticular, the last packet will often appear to  be  lost,	 because  even
       though  it  reaches  the	 destination host, there's no way to know that
       because no ICMP message is sent back.   In  the	TCP  case,  traceroute
       should  listen  for a RST from the destination host (or an intermediate
       router that's filtering packets), but this is not implemented yet.

       Please send bug reports to

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

4.3 Berkeley Distribution      19 February 2008			 TRACEROUTE(8)

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