Provided by: iftop_1.0~pre4-4_amd64 bug


       iftop - display bandwidth usage on an interface by host


       iftop -h | [-nNpblBP] [-i interface] [-f filter code] [-F net/mask] [-G net6/mask6]


       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
              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 STDOUT.


       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

       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 supported:

       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

       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 direction.

       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

       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 <>


       $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 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
       See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program;
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