traceroute(8) — Linux manual page


TRACEROUTE(8)             Traceroute For Linux             TRACEROUTE(8)

NAME         top

       traceroute - print the route packets trace to network host

SYNOPSIS         top

       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 waittimes] [-z sendwait] [-UL] [-D]
               [-P proto] [--sport=port] [-M method] [-O mod_options]
               [--mtu] [--back]
               host [packet_len]
       traceroute6  [options]

DESCRIPTION         top

       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
       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  certain  timeout,  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  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

OPTIONS         top

       --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 IPv4.

       -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 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
              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 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 and others specifies just the (constant)
              destination port to connect.

       -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 max[,here,near], --wait=max[,here,near]
              Determines how long to wait for a response to a probe.

              There are three (in general) float values separated by a
              comma (or a slash).  Max specifies the maximum time (in
              seconds, default 5.0) to wait, in any case.

              Traditional traceroute implementation always waited whole
              max seconds for any probe. But if we already have some
              replies from the same hop, or even from some next hop, we
              can use the round trip time of such a reply as a hint to
              determine the actual reasonable amount of time to wait.

              The optional here (default 3.0) specifies a factor to
              multiply the round trip time of an already received
              response from the same hop. The resulting value is used as
              a timeout for the probe, instead of (but no more than)
              max.  The optional near (default 10.0) specifies a similar
              factor for a response from some next hop.  (The time of
              the first found result is used in both cases).

              First, we look for the same hop (of the probe which will
              be printed first from now).  If nothing found, then look
              for some next hop. If nothing found, use max.  If here
              and/or near have zero values, the corresponding
              computation is skipped.
              Here and near are always set to zero if only max is
              specified (for compatibility with previous versions).

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

       -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, --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 messages.

       -e, --extensions
              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 / ). The Interface Information (rfc5837) is
              shown parsed as well, in a following form:
              {INC|SUB|OUT|NXT}:index,IP_addr,"name",mtu=MTU (all four
              fields may be missing).

       -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 are additional options intended for advanced usage (such as
       alternate trace methods etc.):

              Chooses the source port to use. Implies -N 1 -w 5 .
              Normally source ports (if applicable) are chosen by the

              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,

       -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 (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
       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, for IPv6 since 3.11), which supports new dgram
       icmp (or "ping") sockets. To allow such sockets, sysadmin should
       provide 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 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

              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 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 fastopen tcp option (when syn), for initial cookie
              negotiation only.

              Use value of num (or unchanged) for maxseg tcp header
              option (when syn), and discover its clamping along the
              path being traced.  New changed mss is printed once in a
              form of M=NUM at the first probe on which it was detected.
              Note, some routers may return too short original fragment
              in the time exceeded message, making the check impossible.
              Besides that the responses may come in a different order.
              All this can lead to a later place of the report (using
              -N 1 can help for the order).

       info   Print tcp flags and supported options of final tcp replies
              when the target host is reached.  Allows to determine
              whether an application listens the port and other useful
              things.  Supported tcp options are all that can be set by
              -T -O, ie.  mss, sack, timestamps, window_scaling and
              fastopen, with the similar output format (a value for mss
              and just presence for others).

       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,
       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 -w 5 .

              Use IP protocol proto (default 253).

NOTES         top

       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.

       To avoid an extra waiting, we use adaptive algorithm for timeouts
       (see -w option for more info). It can lead to premature expiry
       (especially when response times differ at times) and printing "*"
       instead of a time. In such a case, switch this algorithm off, by
       specifying -w with the desired timeout only (for example, -w 5).

       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         top

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

COLOPHON         top

       This page is part of the traceroute (trace route to network host)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report
       for this manual page, send it to  This page was obtained
       from the tarball traceroute-2.1.5.tar.gz fetched from
       on 2024-06-14.  If you discover any rendering problems in this
       HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to

Traceroute                   11 October 2006               TRACEROUTE(8)

Pages that refer to this page: tracepath(8)