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

NAME
       iftop - display bandwidth usage on an interface by host

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

DESCRIPTION
       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 run

       ning.

       By  default,  iftop counts all IP packets that pass through the filter, and the direction of the packet is determined ac

       cording 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 10.0.0.0/255.0.0.0 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?

OPTIONS
       -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  evalu

              ated 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 /255.255.255.0, 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 numeri

              cal 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.

DISPLAY
       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  trans

       ferred (after filtering), and total transfer rates averaged over 2s, 10s and 40s.

SOURCE / DEST AGGREGATION
       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.

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

DISPLAY TYPE
       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.

DISPLAY ORDER
       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 re

       spectively.

DISPLAY FILTERING
       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 fil

       ter  code,  and does not affect what is actually captured.  Display filters DO NOT affect the totals at the bottom of the
       screen.

PAUSE DISPLAY / FREEZE ORDER
       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.

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

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

CONFIG FILE
       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, regard

              less 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  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  to

       tals.

       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 en

       tries 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.

FILES
       ~/.iftoprc
              Configuration file for iftop.

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

AUTHOR
       Paul Warren 

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

COPYING
       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  war

       ranty 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.

                                                                                                                        IFTOP(8)

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