Provided by: iftop_1.0~pre2-5_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.

       -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


       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 1.27 2010/11/27 11:06:12 pdw Exp $


       This program is free software; you can redistribute it and/or modify it under the terms of
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       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.

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       if not, write to the Free Software Foundation, Inc., 675 Mass Ave,  Cambridge,  MA  02139,