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TRACEROUTE(1)                          Traceroute For Linux                         TRACEROUTE(1)

       traceroute - print the route packets trace to network host

       traceroute [-46dFITUnreAV] [-f first_ttl] [-g gate,...]
               [-i device] [-m max_ttl] [-p port] [-s src_addr]
               [-q nqueries] [-N squeries] [-t tos]
               [-l flow_label] [-w waittime] [-z sendwait] [-UL] [-D]
               [-P proto] [--sport=port] [-M method] [-O mod_options]
               [--mtu] [--back]
               host [packet_len]
       traceroute6  [options]
       tcptraceroute  [options]
       lft  [options]

       traceroute tracks the route packets taken from an IP network on their way to a given host.
       It utilizes the IP protocol's time to live (TTL) field and  attempts  to  elicit  an  ICMP
       TIME_EXCEEDED response from each gateway along the path to the host.

       traceroute6 is equivalent to traceroute -6

       tcptraceroute is equivalent to traceroute -T

       lft  ,  the  Layer  Four  Traceroute,  performs a TCP traceroute, like traceroute -T , but
       attempts to provide compatibility with  the  original  such  implementation,  also  called

       The  only  required  parameter  is  the  name or IP address of the destination host .  The
       optional packet_len`gth is the total size of the probing packet (default 60 bytes for IPv4
       and  80 for IPv6). The specified size can be ignored in some situations or increased up to
       a minimal value.

       This program attempts to trace the route an IP packet would follow to some  internet  host
       by  launching  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" (or TCP reset), which means we got to the
       "host", or hit a max (which defaults to 30 hops). Three probes (by default)  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. The address  can  be  followed  by  additional  information  when
       requested. If the probe answers come from different gateways, the address of each respond‐
       ing system will be printed.  If there is no response within a 5.0  seconds  (default),  an
       "*" (asterisk) is printed for that probe.

       After  the trip time, some additional annotation can be printed: !H, !N, or !P (host, net‐
       work or protocol unreachable), !S (source route failed),  !F  (fragmentation  needed),  !X
       (communication  administratively  prohibited),  !V (host precedence violation), !C (prece‐
       dence cutoff in effect), or !<num> (ICMP unreachable  code  <num>).   If  almost  all  the
       probes result in some kind of unreachable, traceroute will give up and exit.

       We  don't  want  the destination host to process the UDP probe packets, so the destination
       port is set to an unlikely value (you can change it with the -p flag). There is no such  a
       problem  for  ICMP or TCP tracerouting (for TCP we use half-open technique, which prevents
       our probes to be seen by applications on the destination host).

       In the modern network environment the traditional traceroute methods  can  not  be  always
       applicable,  because of widespread use of firewalls.  Such firewalls filter the "unlikely"
       UDP ports, or even ICMP echoes.  To solve this, some additional tracerouting  methods  are
       implemented  (including tcp), see LIST OF AVAILABLE METHODS below. Such methods try to use
       particular protocol and source/destination port, in order to bypass firewalls (to be  seen
       by firewalls just as a start of allowed type of a network session).

       --help Print help info and exit.

       -4, -6 Explicitly  force  IPv4  or  IPv6 tracerouting. By default, the program will try to
              resolve the name given, and  choose  the  appropriate  protocol  automatically.  If
              resolving  a  host  name  returns both IPv4 and IPv6 addresses, traceroute will use

       -I, --icmp
              Use ICMP ECHO for probes

       -T, --tcp
              Use TCP SYN for probes

       -d, --debug
              Enable socket level debugging (when the Linux kernel supports it)

       -F, --dont-fragment
              Do not fragment probe packets. (For IPv4 it also sets DF bit, which tells  interme‐
              diate routers not to fragment remotely as well).

              Varying  the  size  of the probing packet by the packet_len command line parameter,
              you can manually obtain information about the MTU of individual network  hops.  The
              --mtu option (see below) tries to do this automatically.

              Note, that non-fragmented features (like -F or --mtu) work properly since the Linux
              kernel 2.6.22 only.  Before that version, IPv6 was always  fragmented,  IPv4  could
              use  the  once  the  discovered final mtu only (from the route cache), which can be
              less than the actual mtu of a device.

       -f first_ttl, --first=first_ttl
              Specifies with what TTL to start. Defaults to 1.

       -g gateway, --gateway=gateway
              Tells traceroute to add an IP source routing option to  the  outgoing  packet  that
              tells  the  network to route the packet through the specified gateway (most routers
              have disabled source routing for security reasons).  In general, several  gateway's
              is  allowed  (comma separated). For IPv6, the form of num,addr,addr...  is allowed,
              where num is a route header type (default is type 2). Note the type 0 route  header
              is now deprecated (rfc5095).

       -i interface, --interface=interface
              Specifies  the  interface through which traceroute should send packets. By default,
              the interface is selected according to the routing table.

       -m max_ttl, --max-hops=max_ttl
              Specifies the maximum number of  hops  (max  time-to-live  value)  traceroute  will
              probe. The default is 30.

       -N squeries, --sim-queries=squeries
              Specifies  the  number  of  probe packets sent out simultaneously.  Sending several
              probes concurrently can speed up traceroute considerably. The default value is 16.
              Note that some routers and hosts can use ICMP rate throttling. In such a  situation
              specifying too large number can lead to loss of some responses.

       -n     Do not try to map IP addresses to host names when displaying them.

       -p port, --port=port
              For  UDP tracing, specifies the destination port base traceroute will use (the des‐
              tination port number will be incremented by each probe).
              For ICMP tracing, specifies the initial ICMP sequence value  (incremented  by  each
              probe too).
              For  TCP and others specifies just the (constant) destination port to connect. When
              using the tcptraceroute wrapper, -p specifies the source port.

       -t tos, --tos=tos
              For IPv4, set the Type of Service (TOS) and Precedence value. Useful values are  16
              (low  delay) and 8 (high throughput). Note that in order to use some TOS precedence
              values, you have to be super user.
              For IPv6, set the Traffic Control value.

       -l flow_label, --flowlabel=flow_label
              Use specified flow_label for IPv6 packets.

       -w waittime, --wait=waittime
              Set the time (in seconds) to wait for a response to a probe (default 5.0 sec).

       -q nqueries, --queries=nqueries
              Sets the number of probe packets per hop. The default is 3.

       -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.

       -s source_addr, --source=source_addr
              Chooses an alternative source address. Note that you must select the address of one
              of the interfaces.  By default, the address of the outgoing interface is used.

       -z sendwait, --sendwait=sendwait
              Minimal time interval between probes (default 0).  If the value is  more  than  10,
              then  it  specifies a number in milliseconds, else it is a number of seconds (float
              point values allowed too).  Useful when some routers use rate-limit for  ICMP  mes‐

       -e, --extensions
              Show ICMP extensions (rfc4884). The general form is CLASS/TYPE: followed by a hexa‐
              decimal   dump.    The   MPLS   (rfc4950)   is   shown   parsed,   in    a    form:
              MPLS:L=label,E=exp_use,S=stack_bottom,T=TTL (more objects separated by / ).

       -A, --as-path-lookups
              Perform  AS path lookups in routing registries and print results directly after the
              corresponding addresses.

       -V, --version
              Print the version and exit.

       There is a couple of additional options, intended for an  advanced  usage  (another  trace
       methods etc.):

              Chooses  the  source port to use. Implies -N 1.  Normally source ports (if applica‐
              ble) are chosen by the system.

              Set the firewall mark for outgoing packets (since the Linux kernel 2.6.25).

       -M method, --module=name
              Use specified method for traceroute operations. Default traditional udp method  has
              name default, icmp (-I) and tcp (-T) have names icmp and tcp respectively.
              Method-specific  options  can  be  passed  by  -O .  Most methods have their simple
              shortcuts, (-I means -M icmp, etc).

       -O option, --options=options
              Specifies some method-specific option. Several options are separated by  comma  (or
              use several -O on cmdline).  Each method may have its own specific options, or many
              not have them at all.  To print information about available options, use -O help.

       -U, --udp
              Use UDP to particular destination port for tracerouting (instead of increasing  the
              port per each probe). Default port is 53 (dns).

       -UL    Use UDPLITE for tracerouting (default port is 53).

       -D, --dccp
              Use DCCP Requests for probes.

       -P protocol, --protocol=protocol
              Use  raw  packet  of  specified  protocol for tracerouting. Default protocol is 253

       --mtu  Discover MTU along the path being traced. Implies -F -N 1.  New mtu is printed once
              in  a  form  of  F=NUM  at  the  first probe of a hop which requires such mtu to be
              reached. (Actually, the correspond "frag needed" icmp message normally is  sent  by
              the previous hop).

              Note,  that  some routers might cache once the seen information on a fragmentation.
              Thus you can receive the final mtu from a closer hop.  Try to  specify  an  unusual
              tos by -t , this can help for one attempt (then it can be cached there as well).
              See -F option for more info.

       --back Print  the  number of backward hops when it seems different with the forward direc‐
              tion. This number is guessed in assumption that remote hops send reply packets with
              initial  ttl set to either 64, or 128 or 255 (which seems a common practice). It is
              printed as a negate value in a form of '-NUM' .

       In general, a particular traceroute method may have to be chosen by -M name, but  most  of
       the methods have their simple cmdline switches (you can see them after the method name, if

       The traditional, ancient method of tracerouting. Used by default.

       Probe packets  are  udp  datagrams  with  so-called  "unlikely"  destination  ports.   The
       "unlikely" port of the first probe is 33434, then for each next probe it is incremented by
       one. Since the ports are expected to be unused,  the  destination  host  normally  returns
       "icmp unreach port" as a final response.  (Nobody knows what happens when some application
       listens for such ports, though).

       This method is allowed for unprivileged users.

   icmp       -I
       Most usual method for now, which uses icmp echo packets for probes.
       If you can ping(8) the destination host, icmp tracerouting is applicable as well.

       This method may be allowed for unprivileged users since the kernel 3.0 (IPv4 only),  which
       supports  new  dgram icmp (or "ping") sockets. To allow such sockets, sysadmin should pro‐
       vide net/ipv4/ping_group_range sysctl range to match any group of the user.

       raw    Use only raw sockets (the traditional way).
              This way is tried first by default (for compatibility reasons), then new dgram icmp
              sockets as fallback.

       dgram  Use only dgram icmp sockets.

   tcp        -T
       Well-known modern method, intended to bypass firewalls.
       Uses the constant destination port (default is 80, http).

       If  some  filters  are  present in the network path, then most probably any "unlikely" udp
       ports (as for default method) or even icmp echoes (as for icmp) are  filtered,  and  whole
       tracerouting  will  just  stop at such a firewall.  To bypass a network filter, we have to
       use only allowed protocol/port combinations. If we trace for some, say,  mailserver,  then
       more likely -T -p 25 can reach it, even when -I can not.

       This method uses well-known "half-open technique", which prevents applications on the des‐
       tination host from seeing our probes at all.  Normally, a tcp syn is  sent.  For  non-lis‐
       tened  ports  we receive tcp reset, and all is done. For active listening ports we receive
       tcp syn+ack, but answer by tcp reset (instead of expected tcp ack), this  way  the  remote
       tcp session is dropped even without the application ever taking notice.

       There is a couple of options for tcp method:

              Sets specified tcp flags for probe packet, in any combination.

              Sets the flags field in the tcp header exactly to num.

       ecn    Send  syn  packet with tcp flags ECE and CWR (for Explicit Congestion Notification,

              Use the corresponding tcp header option in the outgoing probe packet.

       sysctl Use current sysctl (/proc/sys/net/*) setting for the tcp header options  above  and
              ecn.  Always set by default, if nothing else specified.

              Use value of num for maxseg tcp header option (when syn).

       info   Print  tcp  flags  of final tcp replies when the target host is reached.  Allows to
              determine whether an application listens the port and other useful things.

       Default options is syn,sysctl.

       An initial implementation of tcp method, simple using connect(2) call, which does full tcp
       session  opening.  Not  recommended  for  normal use, because a destination application is
       always affected (and can be confused).

   udp        -U
       Use udp datagram with constant destination port (default 53, dns).
       Intended to bypass firewall as well.

       Note, that unlike in tcp method, the correspond application on the destination host always
       receive our probes (with random data), and most can easily be confused by them. Most cases
       it will not respond to our packets though, so we will never  see  the  final  hop  in  the
       trace. (Fortunately, it seems that at least dns servers replies with something angry).

       This method is allowed for unprivileged users.

   udplite    -UL
       Use udplite datagram for probes (with constant destination port, default 53).

       This method is allowed for unprivileged users.

              Set udplite send coverage to num.

   dccp    -D
       Use DCCP Request packets for probes (rfc4340).

       This  method uses the same "half-open technique" as used for TCP.  The default destination
       port is 33434.


              Set DCCP service code to num (default is 1885957735).

   raw        -P proto
       Send raw packet of protocol proto.
       No protocol-specific headers are used, just IP header only.
       Implies -N 1.

              Use IP protocol proto (default 253).

       To speed up work, normally several probes are sent simultaneously.  On the other hand,  it
       creates a "storm of packages", especially in the reply direction. Routers can throttle the
       rate of icmp responses, and some of replies can be lost. To avoid this, decrease the  num‐
       ber  of  simultaneous  probes, or even set it to 1 (like in initial traceroute implementa‐
       tion), i.e.  -N 1

       The final (target) host can drop some of the simultaneous probes, and  might  even  answer
       only  the  latest ones. It can lead to extra "looks like expired" hops near the final hop.
       We use a smart algorithm to auto-detect such a situation, but if it cannot  help  in  your
       case, just use -N 1 too.

       For  even greater stability you can slow down the program's work by -z option, for example
       use -z 0.5 for half-second pause between probes.

       If some hops report nothing for every method, the last chance to obtain  something  is  to
       use ping -R command (IPv4, and for nearest 8 hops only).

       ping(8), ping6(8), tcpdump(8), netstat(8)

Traceroute                               11 October 2006                            TRACEROUTE(1)

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