iftop - display bandwidth usage on an interface by host


   iftop -h | [-nNpblBP] [-i interface] [-f filter code] [-F net/mask] [-G


   iftop listens to network traffic on a named interface, or on the  first
   interface it can find which looks like an external interface if none is
   specified, and displays a table of current bandwidth usage by pairs  of
   hosts.   iftop  must  be run with sufficient permissions to monitor all
   network traffic on the interface; see pcap(3) for more information, but
   on most systems this means that it must be run as root.

   By  default, iftop will look up the hostnames associated with addresses
   it finds in packets. This can cause substantial traffic of itself,  and
   may  result in a confusing display. You may wish to suppress display of
   DNS traffic by using filter code such as not port domain, or switch  it
   off  entirely, by using the -n option or by pressing r when the program
   is running.

   By default, iftop counts all IP packets that pass through  the  filter,
   and  the  direction  of  the  packet  is  determined  according  to the
   direction the packet is moving across  the  interface.   Using  the  -F
   option it is possible to get iftop to show packets entering and leaving
   a given network.  For example, iftop -F will analyse
   packets flowing in and out of the 10.* network.

   Some other filter ideas:

   not ether host ff:ff:ff:ff:ff:ff
          Ignore ethernet broadcast packets.

   port http and not host webcache.example.com
          Count  web  traffic  only, unless it is being directed through a
          local web cache.

   icmp   How much bandwidth are users wasting trying to  figure  out  why
          the network is slow?


   -h     Print a summary of usage.

   -n     Don't do hostname lookups.

   -N     Do not resolve port number to service names

   -p     Run  in  promiscuous  mode,  so that traffic which does not pass
          directly through the specified interface is also counted.

   -P     Turn on port display.

   -l     Display and count datagrams addressed to or from link-local IPv6
          addresses.  The default is not to display that address category.

   -b     Don't display bar graphs of traffic.

   -m limit
          Set  the  upper  limit  for the bandwidth scale.  Specified as a
          number with a 'K', 'M' or 'G' suffix.

   -B     Display bandwidth rates in bytes/sec rather than bits/sec.

   -i interface
          Listen to packets on interface.

   -f filter code
          Use filter code to select the packets to count. Only IP  packets
          are  ever counted, so the specified code is evaluated as (filter
          code) and ip.

   -F net/mask
          Specifies an IPv4 network for traffic analysis.   If  specified,
          iftop  will  only  include  packets  flowing in to or out of the
          given network, and packet direction is  determined  relative  to
          the  network  boundary,  rather  than to the interface.  You may
          specify mask as a dotted quad, such as /, or  as  a
          single  number specifying the number of bits set in the netmask,
          such as /24.

   -G net6/mask6
          Specifies an IPv6 network for traffic  analysis.  The  value  of
          mask6  can be given as a prefix length or as a numerical address
          string for more compound bitmasking.

   -c config file
          Specifies an alternate config file.   If  not  specified,  iftop
          will  use  ~/.iftoprc if it exists.  See below for a description
          of config files

   -t text output mode
          Use text interface without  ncurses  and  print  the  output  to


   When  running, iftop uses the whole screen to display network usage. At
   the top of the display is a logarithmic scale for the bar  graph  which
   gives a visual indication of traffic.

   The main part of the display lists, for each pair of hosts, the rate at
   which data has been sent and received over the preceding 2, 10  and  40
   second intervals. The direction of data flow is indicated by arrows, <=
   and =>. For instance,

   foo.example.com  =>  bar.example.com      1Kb  500b   100b
                    <=                       2Mb    2Mb    2Mb

   shows,  on  the   first   line,   traffic   from   foo.example.com   to
   bar.example.com;  in  the  preceding  2 seconds, this averaged 1Kbit/s,
   around half that amount over the preceding 10s, and  a  fifth  of  that
   over  the  whole  of  the last 40s. During each of those intervals, the
   data sent in the other direction  was  about  2Mbit/s.  On  the  actual
   display,  part  of each line is inverted to give a visual indication of
   the 10s average of traffic.  You might expect  to  see  something  like
   this  where  host foo is making repeated HTTP requests to bar, which is
   sending data back which saturates a 2Mbit/s link.

   By default, the pairs of hosts responsible for  the  most  traffic  (10
   second average) are displayed at the top of the list.

   At  the bottom of the display, various totals are shown, including peak
   traffic over the last 40s, total traffic transferred (after filtering),
   and total transfer rates averaged over 2s, 10s and 40s.


   By  pressing s or d while iftop is running, all traffic for each source
   or destination will be aggregated together.  This is most  useful  when
   iftop is run in promiscuous mode, or is run on a gateway machine.


   S or D toggle the display of source and destination ports respectively.
   p will toggle port display on/off.


   t cycles through the  four  line  display  modes;  the  default  2-line
   display, with sent and received traffic on separate lines, and 3 1-line
   displays, with sent, received, or total traffic shown.


   By default, the display is ordered according to the  10s  average  (2nd
   column).   By pressing 1, 2 or 3 it is possible to sort by the 1st, 2nd
   or 3rd column.   By pressing < or >  the  display  will  be  sorted  by
   source or destination hostname respectively.


   l  allows you to enter a POSIX extended regular expression that will be
   used to filter hostnames shown in the display.  This is a good  way  to
   quickly  limit what is shown on the display.  Note that this happens at
   a much later stage than filter  code,  and  does  not  affect  what  is
   actually  captured.   Display  filters  DO NOT affect the totals at the
   bottom of the screen.


   P will pause the current display.

   o will freeze the current screen order.  This has the side effect  that
   traffic  between  hosts not shown on the screen at the time will not be
   shown at all, although it will be included in the totals at the  bottom
   of the screen.


   j  and k will scroll the display of hosts.  This feature is most useful
   when the display order is frozen (see above).


   f allows you to edit the filter code whilst iftop  running.   This  can
   lead to some unexpected behaviour.


   iftop  can read its configuration from a config file.  If the -c option
   is not specified, iftop will attempt to  read  its  configuration  from
   ~/.iftoprc,  if  it  exists.   Any  command line options specified will
   override settings in the config file.

   The config file consists of one configuration directive per line.  Each
   directive is a name value pair, for example:

   interface: eth0

   sets  the  network  interface.   The  following  config  directives are

   interface: if
          Sets the network interface to if.

   dns-resolution: (yes|no)
          Controls reverse lookup of IP addresses.

   port-resolution: (yes|no)
          Controls conversion of port numbers to service names.

   filter-code: bpf
          Sets the filter code to bpf.

   show-bars: (yes|no)
          Controls display of bar graphs.

   promiscuous: (yes|no)
          Puts the interface into promiscuous mode.

   port-display: (off|source-only|destination-only|on)
          Controls display of port numbers.

   link-local: (yes|no)
          Determines displaying of link-local IPv6 addresses.

   hide-source: (yes|no)
          Hides source host names.

   hide-destination: (yes|no)
          Hides destination host names.

   use-bytes: (yes|no)
          Use bytes for bandwidth display, rather than bits.

   sort: (2s|10s|40s|source|destination)
          Sets which column is used to sort the display.

   line-display: (two-line|one-line-both|one-line-sent|one-line-received)
          Controls the appearance of each item in the display.

   show-totals: (yes|no)
          Shows cumulative total for each item.

   log-scale: (yes|no)
          Use a logarithmic scale for bar graphs.

   max-bandwidth: bw
          Fixes the maximum for the bar graph scale  to  bw,  e.g.  "10M".
          Note  that the value has to always be in bits, regardless if the
          option to display in bytes has been chosen.

   net-filter: net/mask
          Defines an IP network boundary for determining packet direction.

   net-filter6: net6/mask6
          Defines  an  IPv6  network  boundary  for   determining   packet

   screen-filter: regexp
          Sets a regular expression to filter screen output.

QUIRKS (aka they're features, not bugs)

   There are some circumstances in which iftop may not do what you expect.
   In most cases what it is doing is logical, and we believe it is correct
   behaviour,   although   I'm   happy  to  hear  reasoned  arguments  for
   alternative behaviour.

   Totals don't add up

   There are several reasons why the totals may not appear to add up.  The
   most  obvious  is  having a screen filter in effect, or screen ordering
   frozen.  In this case some captured information is not being  shown  to
   you, but is included in the totals.

   A  more subtle explanation comes about when running in promiscuous mode
   without specifying a -F option.  In this case there is no easy  way  to
   assign  the  direction  of  traffic between two third parties.  For the
   purposes of the main display this is done in an arbitrary  fashion  (by
   ordering  of  IP  addresses),  but  for  the sake of totals all traffic
   between other hosts is accounted as incoming, because that's what it is
   from  the point of view of your interface.  The -F option allows you to
   specify an arbitrary network boundary,  and  to  show  traffic  flowing
   across it.

   Peak totals don't add up

   Again,  this  is  a  feature.   The  peak sent and peak received didn't
   necessarily happen at the same time.  The peak total is the maximum  of
   sent plus received in each captured time division.

   Changing the filter code doesn't seem to work

   Give  it  time.  Changing the filter code affects what is captured from
   the time that you entered it, but most of what is  on  the  display  is
   based  on  some  fraction  of  the last 40s window of capturing.  After
   changing the filter there may  be  entries  on  the  display  that  are
   disallowed  by the current filter for up to 40s.  DISPLAY FILTERING has
   immediate effect and does not affect what is captured.


          Configuration file for iftop.


   tcpdump(8), pcap(3), driftnet(1).


   Paul Warren <pdw@ex-parrot.com>


   $Id: iftop.8,v 1.31 2014/01/05 17:22:39 pdw Exp $


   This program is free software; you can redistribute it and/or modify it
   under  the  terms of the GNU General Public License as published by the
   Free Software Foundation; either version 2 of the License, or (at  your
   option) any later version.

   This  program  is  distributed  in the hope that it will be useful, but
   WITHOUT  ANY  WARRANTY;  without   even   the   implied   warranty   of
   General Public License for more details.

   You should have received a copy of the GNU General Public License along
   with this program; if not, write to the Free Software Foundation, Inc.,
   51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.


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