xenial (1) lft.db.1.gz

Provided by: traceroute_2.0.21-1_amd64 bug

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] [-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_EXCEEDED  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 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
       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

       --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. When using 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 waittime, --wait=waittime
              Set the time (in seconds) to wait for a response to a probe (default 5.0 sec).

       -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.):

       --sport=port
              Chooses the source port to use. Implies -N 1.  Normally source ports (if applicable) 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 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' .

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 only),  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 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:

       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.

       mss=num
              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.

   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.
       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)