TRACEROUTE(8)           OpenBSD System Manager's Manual          TRACEROUTE(8)

NAME
     traceroute - print the route packets take to network host

SYNOPSIS
     traceroute [-cDdIlnrSv] [-f first_ttl] [-g gateway_addr] [-m max_ttl]
                [-P proto] [-p port] [-q nqueries] [-s src_addr] [-t tos]
                [-V rdomain] [-w waittime] host [packetsize]

DESCRIPTION
     The Internet is a large and complex aggregation of network hardware, con-
     nected together by gateways.  Tracking the route one's packets follow (or
     finding the miscreant gateway that's discarding your packets) can be dif-
     ficult.  traceroute utilizes the IP protocol `time to live' field and at-
     tempts 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.

     The options are as follows:

     -c      Do not increment the destination port number in successive UDP
             packets.  Rather, all UDP packets will have the same destination
             port, as set via the -p flag (or 33434 if none is specified).

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

     -d      Turn on socket-level debugging.

     -f first_ttl
             Set the first time-to-live used in outgoing probe packets.  The
             effect is that the first first_ttl - 1 hosts will be skipped in
             the output of traceroute.  The default value is 1 (skip no
             hosts).

     -g gateway_addr
             Add gateway_addr to the list of addresses in the IP Loose Source
             Record Route (LSRR) option.  If no gateways are specified, the
             LSRR option is omitted.

     -I      Equivalent to -P 1.  Used for compatibility with other OSes.

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

     -m max_ttl
             Set the max time-to-live (max number of hops) used in outgoing
             probe packets.  The default is the value of the system's
             net.inet.ip.ttl MIB variable, which defaults to 64.

     -n      Print hop addresses numerically rather than symbolically and nu-
             merically (saves a nameserver address-to-name lookup for each
             gateway found on the path).

     -P proto
             Change the protocol being used from UDP to a numeric protocol or
             a name as specified in /etc/protocols.  This will not work reli-
             ably for most protocols.  If set to 1 (ICMP), then ICMP Echo Re-
             quest messages will be used (same as ping(8)).

     -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*nqueries-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 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 corresponds to the
             SO_DONTROUTE socket option; it 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 a routing daemon).

     -S      Print how many probes were not answered for each hop.

     -s src_addr
             Use the following IP address (which must be given as an IP num-
             ber, 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
             and the user is not the superuser, an error is returned and noth-
             ing 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 running a
             4.3BSD-Tahoe or later system, this may be academic since the nor-
             mal 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 rdomain
             Set the routing domain.  The default is 0.

     -v      Verbose output.  Received ICMP packets other than TIME_EXCEEDED
             and UNREACHABLEs are listed.

     -w waittime
             Set the time (in seconds) to wait for a response to a probe (de-
             fault 5).

     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 out 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 64 hops and 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 ad-
     dress of each responding system will be printed.  If there is no response
     within a 5 second 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:

           $ traceroute nis.nsf.net.
           traceroute to nis.nsf.net (35.1.1.48), 64 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:

           $ traceroute allspice.lcs.mit.edu.
           traceroute to allspice.lcs.mit.edu (18.26.0.115), 64 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 un-
     reachable 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 ex-
     actly 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 (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, !P (got a host,
     network or protocol unreachable, respectively), !A, !C (access to the
     network or host, respectively, is prohibited), !X (communication adminis-
     tratively prohibited by filtering), !S or !F (source route failed or
     fragmentation needed - neither of these should ever occur and the associ-
     ated gateway is busted if you see one), !U (destination network or host
     unknown), !T (destination network or host unreachable for TOS), !<code>
     (other ICMP unreachable code).  If almost all the probes result in some
     kind of unreachable, traceroute will give up and exit.

           $ traceroute -g 10.3.0.5 128.182.0.0

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

           $ traceroute -g 192.5.146.4 -g 10.3.0.5 35.0.0.0

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

     This program is intended for use in network testing, measurement and man-
     agement.  It should be used primarily for manual fault isolation.  Be-
     cause of the load it could impose on the network, it is unwise to use
     traceroute during normal operations or from automated scripts.

SEE ALSO
     netstat(1), ping(8)

HISTORY
     The very first traceroute (never released) used ICMP ECHO_REQUEST data-
     grams as probe packets.  During the first night of testing it was discov-
     ered that more than half the router vendors of the time would not return
     an ICMP TIME_EXCEEDED for an ECHO_REQUEST.  traceroute was then changed
     to use UDP probe packets.  Most modern TCP/IP implementations will now
     generate an ICMP error message to ICMP query messages, and the option to
     use ECHO_REQUEST probes was re-implemented.

     The traceroute command first appeared in 4.4BSD.

AUTHORS
     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.

OpenBSD 4.7                      July 6, 2009                                4
