man > traceroute-nanog(1)

TRACEROUTE(1)                           Traceroute For Linux                           TRACEROUTE(1)

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 waittimes] [-z sendwait] [-UL] [-D]
               [-P proto] [--sport=port] [-M method] [-O mod_options]
               [--mtu] [--back]
               host [packet_len]
       traceroute6  [options]
       tcptraceroute  [options]
       lft  [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_EX‐
       CEEDED response from each gateway along the path to the host.

       traceroute6 is equivalent to traceroute -6

       tcptraceroute is equivalent to traceroute -T

       lft , the Layer Four Traceroute, performs a TCP traceroute, like traceroute -T , but attempts
       to provide compatibility with the original such implementation, also called "lft".

       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 ex‐
       ceeded" reply from a gateway.  We start our probes with a ttl of one and increase by one  un‐
       til  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 an‐
       swers  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 (communica‐
       tion 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 ap‐
       plicable, 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 imple‐
       mented (including tcp), see LIST OF AVAILABLE METHODS below. Such methods try to use particu‐
       lar protocol and source/destination port, in order to bypass firewalls (to be seen  by  fire‐
       walls 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 tracerouting. By default, the program will try to re‐
              solve 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 dis‐
              abled 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 destina‐
              tion 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. When us‐
              ing the tcptraceroute wrapper, -p specifies the source port.

       -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 reason‐
              able 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 time‐
              out  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 hexadec‐
              imal  dump.   The  MPLS  (rfc4950)  is   shown   parsed,   in   a   form:   MPLS:L=la‐
              bel,E=exp_use,S=stack_bottom,T=TTL  (more  objects separated by / ). The Interface In‐
              formation   (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.):

       --sport=port
              Chooses the source port to use. Implies -N 1 -w 5 .  Normally source ports (if applic‐
              able) are chosen by the system.

       --fwmark=mark
              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  short‐
              cuts, (-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' .

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 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 user.
       Options:

       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  tracerout‐
       ing  will  just stop at such a firewall.  To bypass a network filter, we have to use only al‐
       lowed 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 desti‐
       nation 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  ses‐
       sion 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 Congestion 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.

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

       mss=[num]
              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, time‐
              stamps,  window_scaling  and fastopen, with the similar output format (a value for mss
              and just presence for others).

       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 confused).

   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.
       Options:

       coverage=num
              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.

       Options:

       service=num
              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 .
       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.

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

Traceroute                                 11 October 2006                             TRACEROUTE(1)