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IFTOP(8)                                                              IFTOP(8)

       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 sub-
       stantial  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 deter-
       mined 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 dis-
              play 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 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 pos-
       sible  to sort by the 1st, 2nd or 3rd column.   By pressing < or > the display will be sorted by source or des-
       tination 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

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

       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 set-
       tings in the config file.

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

       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 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 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 log-
       ical,  and  we  believe  it is correct behaviour, although I'm happy to hear reasoned arguments for alternative

       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 fil-
       ter there may be entries on the display that are disallowed by the current filter for up to 40s.  DISPLAY  FIL-
       TERING 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 Pub-
       lic 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; if not, write to the
       Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.