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 session).

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

       -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

       -F, --dont-fragment
              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, --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

       -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 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, --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 / ).

       -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 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 (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.

       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

       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

       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 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

   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 -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-2.1.0.tar.gz
       fetched from
       on 2020-11-01.  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: brctl(8)tracepath(8)