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IFTOP(8)							      IFTOP(8)

       iftop - display bandwidth usage on an interface by host

       iftop -h | [-nNpbBP] [-i interface] [-f filter code] [-F net/mask]

       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 bandwith 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.

       -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	 a  network for traffic analysis.  If specified, iftop
	      will only include packets flowing in to or out of the given net‐
	      work, 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.

       -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 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.

       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 cummulative 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"

       net-filter: net/mask
	      Defines an IP 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 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 1.25 2005/12/25 11:50:21 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.,
       675 Mass Ave, Cambridge, MA 02139, USA.

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