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TRACEROUTE(8)                Traceroute For Linux                TRACEROUTE(8)

NAME
       traceroute - print the route packets trace to network host

SYNOPSIS
       traceroute [-46dFITUnrAV] [-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]
               host [packetlen]
       traceroute6  [options]
       tracert  [options]
       tcptraceroute  [options]

DESCRIPTION
       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
       tracert is equivalent to traceroute -I
       tcptraceroute is equivalent to traceroute -T

       The only required parameter is the name or IP address of  the  destina-
       tion  host .  This parameter can be followed by the size of the probing
       packet sent to that host (40 by  default).  Varying  the  size  of  the
       packet  in  conjunction  with  the  -F  parameter can be used to obtain
       information about the MTU of individual network hops. (The size parame-
       ter is useless for TCP probes).

       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.  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 "*" 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
       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 tracer-
       outing (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).

OPTIONS
       --help Print help info and exit.

       -4, -6 Explicitly force IPv4 or IPv6 traceouting. By default, the  pro-
              gram  will  try to resolve the name given, and choose the appro-
              priate 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
              it)

       -F     Set the "Don't Fragment" bit. This  tells  intermediate  routers
              not  to  fragment  the  packet when they find it's too big for a
              network hop's MTU.

       -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  out-
              going  packet that tells the network to route the packet through
              the specified gateway.  Not very useful,  because  most  routers
              have disabled source routing for security reasons.

       -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 con-
              siderably. 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
              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  con-
              nect.

       -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.

       -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.):

       --sport=port
              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 tradi-
              tional 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 sepa-
              rated  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
              (dns).

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

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

LIST OF AVAILABLE METHODS
       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).

   default
       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  lis-
       tens 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 applica-
       ble 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 pro-
       tocol/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:

       syn,ack,fin,rst,psh,urg,ece,cwr
              Sets specified tcp flags for probe packet, in any combination.

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

       ecn    Send syn packet with tcp flags ECE and CWR (for Explicit Conges-
              tion Notification, rfc3168)

       sack,timestamps,window_scaling
              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.

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

       Default options is syn,sysctl.

   tcpconn
       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 con-
       fused).

   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 des-
       tination  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. (For-
       tunately, 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.
       Options:

       coverage=num
              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.
       Options:

       protocol=proto
              Use IP protocol proto (default 253).

NOTES
       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
       only).

SEE ALSO
       ping(8), ping6(8), tracepath(8), netstat(8)

Traceroute                      11 October 2006                  TRACEROUTE(8)

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