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       iftop - display bandwidth usage on an interface by host


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


       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 n 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
              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.

       -b     Don’t display bar graphs of traffic.

       -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  a  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

       -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


       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,  =>      1Kb  500b   100b
                        <=                       2Mb    2Mb    2Mb

       shows,  on  the   first   line,   traffic   from   to;  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.

       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.

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

QUIRKS (aka theyre 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 dont 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 dont 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 doesnt 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 <>


       $Id: iftop.8,v 1.25 2005/12/25 11:50:21 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.,
       675 Mass Ave, Cambridge, MA 02139, USA.