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IFTOP(8)                    System Manager's Manual                   IFTOP(8)

       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 direc‐
       tion 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  STD‐

       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.exam‐
       ple.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  dis‐
       play,  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  actu‐
       ally  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 sup‐

       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  direc‐

       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 alterna‐
       tive 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 nec‐
       essarily 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 disal‐
       lowed by the current filter for up to 40s.  DISPLAY FILTERING has imme‐
       diate 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  MER‐
       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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