Man Linux: Main Page and Category List


       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] [-P proto] [--sport=port] [-M method] [-O mod_options]
               [--mtu] [--back]
               host [packet_len]
       traceroute6  [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
       lft is equivalent to traceroute -t

       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
       responding 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,  network  or  protocol  unreachable),  !S  (source  route
       failed),  !F (fragmentation needed), !X (communication administratively
       prohibited), !V (host precedence violation), !C (precedence  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

       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  traceouting.  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 IPv4.

       -I     Use ICMP ECHO for probes

       -T     Use TCP SYN for probes

       -d     Enable socket level debugging (when the  Linux  kernel  supports

       -F     Do  not  fragment  probe packets. (For IPv4 it also sets DF bit,
              which tells intermediate routers not  to  fragment  remotely  as

              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
              Specifies with what TTL to start. Defaults to 1.

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

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

       -N 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

       -p port
              For  UDP tracing, specifies the destination port base traceroute
              will use (the destination port number  will  be  incremented  by
              each probe).
              For  ICMP  tracing,  specifies  the  initial icmp sequence value
              (incremented by each probe too).
              For TCP  specifies  just  the  (constant)  destination  port  to

       -t 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 precendence values, you have to be
              super user.
              For IPv6, set the Traffic Control value.

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

       -q 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 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.

       -s 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
              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 messages.

       -e     Show ICMP extensions (rfc4884). The general form is  CLASS/TYPE:
              followed  by  a  hexadecimal  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     Perform  AS path lookups in routing registries and print results
              directly after the corresponding addresses.

       -V     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 applicable) are chosen by the system.

       -M method
              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
              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     Use UDP to particular destination port for tracerouting (instead
              of  increasing  the  port  per  each  probe). Default port is 53

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

       -P protocol
              Use raw packet of specified protocol for  tracerouting.  Default
              protocol is 253 (rfc3692).

       --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 direction. 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 present).

       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.

   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 destination host from seeing  our  probes  at  all.
       Normally,  a  tcp  syn  is  sent. For non-listened 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, rfc3168)

              Use the corresponding tcp header option in  the  outgoing  probe

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

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

       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

   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

       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.

   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 number of
       simultaneous probes, or even set it to 1 (like  in  initial  traceroute
       implementation), 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


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