TRACEROUTE(8)		     Traceroute For Linux		 TRACEROUTE(8)



NAME
       traceroute - print the route packets trace to network host

SYNOPSIS
       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]

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

       The only required parameter is the name or IP address of	 the  destina-
       tion host .  The optional packet_len`gth is the total size of the prob-
       ing 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
       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     Do not fragment probe packets. (For IPv4 it also	sets  DF  bit,
	      which  tells  intermediate  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 prop-
	      erly since the Linux kernel 2.6.22 only.	Before	that  version,
	      IPv6  was always fragmented, IPv4 could use the once the discov-
	      ered 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 out-
	      going 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 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.

       -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.):

       --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).

       --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 corre-
	      spond  "frag needed" icmp message normally is sent by the previ-
	      ous 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' .

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), tcpdump(8), netstat(8)



Traceroute			11 October 2006			 TRACEROUTE(8)