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traceroute(8)             BSD System Manager's Manual            traceroute(8)


NAME

     traceroute -- print the route packets take to network host


SYNOPSIS

     traceroute [-adeFISdNnrvx] [-A as_server] [-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]
                [-z pausemsecs] 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
     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 size (in bytes) after the destination host name.

     Other options are:

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

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

     -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 under-
             scores.  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.

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

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

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

     -g gateway
             Specify a loose source route gateway (8 maximum).

     -i iface
             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
             icmp").

     -M first_ttl
             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 max_ttl
             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 proto
             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 formats.
             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 port
             Protocol specific. For UDP and TCP, sets the base 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.

     -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 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,
             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
             hop.

     -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
             4.4BSD 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 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 cal-
             culating 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 check-
             sums and using -x causes them to be calculated). Note that check-
             sums are usually required for the last hop when using ICMP ECHO
             probes ( -I ). So they are always calculated when using ICMP.

     -z pausemsecs
             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 (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 gate-
     ways, 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 nis.nsf.net.
     traceroute to nis.nsf.net (35.1.1.48), 64 hops max, 38 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), 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
     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, or !P (host, net-
     work or protocol unreachable), !S (source route failed), (fragmentation
     needed - the RFC1191 Path MTU Discovery value is displayed), !U or !W
     (destination network/host unknown), !I (source host is isolated), !A
     (communication with destination network administratively prohibited), !Z
     (communication with destination host administratively 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 violation), !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 man-
     agement.  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), traceroute6(8)


BUGS

     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.

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

4.3 Berkeley Distribution        May 29, 2008        4.3 Berkeley Distribution

Mac OS X 10.7 - Generated Sun Sep 4 18:15:56 CDT 2011