NetFlow: installation and configuration of NFDUMP and NfSen on Debian

After the brief overview about the installation of flow-tools and FlowViewer, in this post I’d like to share my experience about the setup of a basic solution based on another pair of tools: NFDUMP and NfSen. As always on my posts, the starting point is a fresh Debian 5.0 setup.

Components used in the solution

As it was for the previous solution, two main components are involved, one to acquire NetFlow data, the other to analyze them in an easy way.

NFDUMP is a suite of tools composed by many programs; nfcapd is one of them and it is the daemon which listens for incoming NetFlow data. It is launched by NfSen.

NfSen is the web based front end we use to analyze NFDUMP NetFlow data. It is splitted up in two parts: a Perl program which runs in the background and launches nfcapd, and some PHP web pages.

The biggest difference between a NFDUMP/NfSen based solution and a flow-tools/FlowViewer solution is that the former does support NetFlow v9, while the latter may result in a simpler and easier tool to work with. Anyway, there is not one perfect solution for all the needs!

In this post I’ll use NFDUMP 1.6.1 and NfSen 1.3.2, the latest stable releases I can find on SourceForge while I’m writing this blog entry; you can find their web pages in the References section of this post. I’ll build them from source code.


Let’s add some tools we’ll need to build the package:

apt-get install gcc flex librrd-dev make

We are ready to start! The steps are very simple: download source code and extract the tar:

cd /usr/local/src/
gzip -dc nfdump-1.6.1.tar.gz | tar -xf -
cd nfdump-1.6.1

In order to use NFDUMP with NfSen we need to enable nfprofile in the configure step; then we have to make && make install it:

./configure --enable-nfprofile 
make install

Now it is ready to be ran.

If we want to use it without NfSen we can stop here and create a simple init.d script to launch NFDUMP at startup; it will acquire NetFlow data and we can use command line tools (such as nfdump) to analyze them. You can find a basic init.d script at the end of this post (“Annex A: stand-alone NFDUMP”).

But that’s not our goal, we want NfSen!


As said, NfSen has a PHP front-end so it needs a web server with PHP support in order to be used. It also uses RRD to store data and paint nice graphs and some Perl modules to produce alerts: let’s satisfy its prerequisites:

apt-get install apache2 libapache2-mod-php5 php5-common libmailtools-perl rrdtool librrds-perl

Now it’s time to download and configure the program:

cd /usr/local/src/
gzip -dc nfsen-1.3.2.tar.gz | tar -xf -
cd nfsen-1.3.2

Once extracted, we have to copy the config file into /etc and modify it:

cp etc/nfsen-dist.conf /etc/nfsen.conf
nano /etc/nfsen.conf

As you can see from the support web page it presents a lot of parameters, but many of them may be left unchanged; in this example I chose to leave as many parameters as possible at their default settings, so we have all the files in a single directory: /data/nfsen. Here the parameters I changed:

$USER    = "www-data";
$WWWUSER  = "www-data";
$WWWGROUP = "www-data";

%sources = (
    'MYROUTER'    => { 'port'    => '9995', 'col' => '#0000ff', 'type' => 'netflow' },


For a better setup I suggest you to read the configuration guide on the project’s web site.

Let’s make the destination directory and complete the installation by running the script:

mkdir -p /data/nfsen
./ /etc/nfsen.conf

We are ready to run the nfsen program and let it executes nfcapd daemon:

cd /data/nfsen/bin
./nfsen start

We can also schedule it to be ran at startup:

ln -s /data/nfsen/bin/nfsen /etc/init.d/nfsen
update-rc.d nfsen defaults 20

It’s ready: point your browser at http://YOUR_IP_ADDRESS/nfsen/nfsen.php and enjoy! Of course, this is just a very basic setup, both NFDUMP and NfSen have many options you can set and use to have better performances and to improve stability and scalability. If you want to go deep into their configuration I suggest you to use the links you can find at the end of this post.

P.S.: Don’t forget to configure your routers to export NetFlow data! ;-)

Annex A: stand-alone NFDUMP

As said, NFDUMP may be used in a stand-alone way, without the help of NfSen.

We just have to build a destination directory for NetFlow data…

mkdir -p /var/flows/MYROUTER
mkdir -p /var/flows/MYSECONDROUTER

and add an init.d script like the following one:

#! /bin/sh
# Provides:          nfcapd
# Required-Start:    $network
# Required-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: netflow capture daemon
# Description:       nfcapd is the netflow capture daemon of the nfdump tools.

# Author: Erik Wenzel <>
# Edited by Pierky for the blog post "NetFlow: installation and configuration of 
# NFDUMP and NfSen on Debian" on

# Do NOT "set -e"

# PATH should only include /usr/* if it runs after the script
DESC="netflow capture daemon"

# Exit if the package is not installed
[ -x "$DAEMON" ] || exit 0

# Load the VERBOSE setting and other rcS variables
. /lib/init/

# Define LSB log_* functions.
# Depend on lsb-base (>= 3.0-6) to ensure that this file is present.
. /lib/lsb/init-functions

# Function that starts the daemon/service
        # Return
        #   0 if daemon has been started
        #   1 if daemon was already running
        #   2 if daemon could not be started
        start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test > /dev/null 
                || return 1
        start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON -- 
                || return 2
        # Add code here, if necessary, that waits for the process to be ready
        # to handle requests from services started subsequently which depend
        # on this one.  As a last resort, sleep for some time.

# Function that stops the daemon/service
        # Return
        #   0 if daemon has been stopped
        #   1 if daemon was already stopped
        #   2 if daemon could not be stopped
        #   other if a failure occurred
        start-stop-daemon --stop --quiet --retry=TERM/30/KILL/5 --pidfile $PIDFILE --name $NAME
        [ "$RETVAL" = 2 ] && return 2
        # Wait for children to finish too if this is a daemon that forks
        # and if the daemon is only ever run from this initscript.
        # If the above conditions are not satisfied then add some other code
        # that waits for the process to drop all resources that could be
        # needed by services started subsequently.  A last resort is to
        # sleep for some time.
        # Disabled second call, because is kills nfsen controlled nfcapd
        #start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec $DAEMON
        #[ "$?" = 2 ] && return 2
        # Many daemons don't delete their pidfiles when they exit.
        rm -f $PIDFILE
        return "$RETVAL"

# Function that sends a SIGHUP to the daemon/service
do_reload() {
        # If the daemon can reload its configuration without
        # restarting (for example, when it is sent a SIGHUP),
        # then implement that here.
        start-stop-daemon --stop --signal 1 --quiet --pidfile $PIDFILE --name $NAME
        return 0

case "$1" in
        [ "$VERBOSE" != no ] && log_daemon_msg "Starting $DESC" "$NAME"
        case "$?" in
                0|1) [ q"$VERBOSE" != qno ] && log_end_msg 0 ;;
                2)   [ p"$VERBOSE" != pno ] && log_end_msg 1 ;;
        [ "$VERBOSE" != no ] && log_daemon_msg "Stopping $DESC" "$NAME"
        case "$?" in
                0|1) [ "r$VERBOSE" != rno ] && log_end_msg 0 ;;
                2) [ "s$VERBOSE" != sno ] && log_end_msg 1 ;;
        # If do_reload() is not implemented then leave this commented out
        # and leave 'force-reload' as an alias for 'restart'.
        #log_daemon_msg "Reloading $DESC" "$NAME"
        #log_end_msg $?
        # If the "reload" option is implemented then remove the
        # 'force-reload' alias
        log_daemon_msg "Restarting $DESC" "$NAME"
        case "$?" in
                case "$?" in
                        0|1) log_end_msg 0 ;;
                        *) log_end_msg 1 ;; # Failed to start
                # Failed to stop
                log_end_msg 1
        #echo "Usage: $SCRIPTNAME {start|stop|restart|reload|force-reload}" >&2
        echo "Usage: $SCRIPTNAME {start|stop|restart|force-reload}" >&2
        exit 3
exit 0

I edited this script starting from the one included in the Debian’s package.

Please note the DATA_BASE_DIR and the DAEMON_ARGS variables. The first contains the base destination directory for our NetFlow data. The second represents arguments we want to use when launching nfcapd; you can add as many -n options as you want, one for each NetFlow source you want to collect data from. Remember: man nfcapd is your friend! ;)


chmod a+x /etc/init.d/nfdump
update-rc.d nfdump defaults 20
/etc/init.d/nfdump start

References NetFlow version 9



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  1. Fred says:


    Is there a way to exploit Netflow v9 with nfsen?

    • pierky says:


      yes, nfsen does support NetFlow v9 fields.

      Basically nfsen puts togheter nfdump command line arguments. You can use them as filter (example: “bgpnext ip″) and you can also use them in the stats. In order to do this you have to edit the /nfsen/details.php file, adding a new entry both in $IPStatOption and $IPStatArg arrays: you have to add a text for the combo box to the former (‘BGP next-hop IP’ in my exampl), and the nfdump corresponding argument to the latter (‘-s nhbip’):

      $IPStatOption = array ( 'Flow Records',
      'Any IP Address', 'SRC IP Address', 'DST IP Address',
      'Any Port', 'SRC Port', 'DST Port',
      'Any AS', 'SRC AS', 'DST AS',
      'Any interface', 'IN interface', 'OUT interface',
      'Proto', 'TOS', 'BGP next-hop IP');

      $IPStatArg = array ( '-s record',
      '-s ip', '-s srcip', '-s dstip',
      '-s port', '-s srcport', '-s dstport',
      '-s as', '-s srcas', '-s dstas',
      '-s if', '-s inif', '-s outif',
      '-s proto', '-s tos', '-s nhbip');

      • Josh Koud says:

        Hi, I couple of questions:

        1) First, I can’t see any information about ipv6 when I use the filter
        ipv6 in Netflow Processing. I am using Nfsen version 1.3.2 and Nfdump
        version 1.6. This is my router configuration:

        interface GigabitEthernet0/2.821
        encapsulation dot1Q 821
        ip address 210.x.x.x 255.x.x.x
        ip flow ingress
        ip pim sparse-dense-mode
        no snmp trap link-status
        ipv6 address X:X:X:X::1/64

        ROUTER#show run | include flow
        ip flow ingress
        ip flow-export source GigabitEthernet0/2.821
        ip flow-export version 9 peer-as
        ip flow-export destination x.x.x.x 2002

        I can only see information about proto 41 (ipv6 encapsulation) but any ipv6 address

        2) There is a way to see mac-address using nfsen?

        3) How can I know if some ip address is using file-sharing programs
        like bit-torrent?

  2. Jochen says:

    Nice blog post. What I really like about nfdump is the tcpdump/libpcap style filters. But I have to admint that I use nfdump/nfsen only for basic stuff like top-talker stats and plotting host-to-host communication relationships in combination with AfterGlow.

    Best Regards,


  3. elena Repi says:

    thank you



  4. [...] This post was mentioned on Twitter by Gerald Scott and Medical Cumulus, Pier Carlo Chiodi. Pier Carlo Chiodi said: New post: NetFlow: installation and configuration of NFDUMP and NfSen on Debian [...]

  5. sharon saadon says:

    If you have the error at the web “Permission denied”
    run the command –
    chmod a+rw /data/nfsen/var/run/nfsen.comm


  6. study4ccie says:

    I am not getting any graphs in the nfsen.php. It says : ‘Error creating Grpahs!’ under DETAILS and ‘No data available’ under HOME page.

    I am able to get the historical IP accounting and other flow data.

    This is not a permissions issue as I have already tried giving 777 permission to the whole directory where the data is..


  7. [...] homepage: Documentation and Howtos: Official Documentation, Nfsen and Nfdump Howto, Tracking incidents with Nfsen, Traffic Classification with Nfsen.Bottom LineOf course there are [...]

  8. fahacz says:

    Thx, probably you howto install bison (apt-get install bison) before compile nfdump, otherwise make fail.

    /bin/bash ../ylwrap grammar.y grammar.c grammar.h y.output grammar.output — yacc -d
    ../ylwrap: řádek 109: yacc: command not found

  9. [...] homepage: Documentation and Howtos: Official Documentation, Nfsen and Nfdump Howto, Tracking incidents with Nfsen, Traffic Classification with [...]

  10. [...] homepage: Documentation and Howtos: Official Documentation, Nfsen and Nfdump Howto, Tracking incidents with Nfsen, Traffic Classification with [...]

  11. netflow

    potencionální tooly Name Language Last update OS Open source web ntop (c) 20120813 v9 n

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