# traceroute

## 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_]
    


## 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
           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



           **--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 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 **/**). 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.):
    
           **--sport** =_port_
                  Chooses the source port to use. Implies **-N 1** -w 5 .
                  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, 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 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.
    
           **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_ , _timestamps_ , _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).
    


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