Skip to main content

Tips and Tricks: Monitoring with NTOP and IFTOP

For monitoring networks I have an old GX260 Dell desktop in the small form factor. Packed into this little device are a couple of network cards, added on are a wireless NIC and an extra USB network device. The purpose? To slot this in between the router and the network and see what's going backwards and forwards - very useful in the situation where a client is hemorrhaging bandwidth and doesn't know why. I'm running Ubuntu 10.04 LTS on it and it behaves very well.

Two of the main tools I use are ntop and iftop. For those of you not familiar with them, ntop monitors a particular interface and creates some nice webpages to be checked by the user in order to see what's going on through the network. iftop is similar but real time and is available through a console - which is the real appeal for me.

The server in question has two internal NICs, both are 100MB cards and are scripted to come up as a transparent bridge - br0. Basically I monitor that bridge and use one of the other interfaces to see what the server is seeing. Here is the script I use (adapted from elsewhere) to bring the bridge up:

slaveIfs="1 2 3 4 6 7 8 9 10";
[ -z "$cmd" ] && cmd="start";
case "$cmd" in
    brctl addbr br0;
    brctl stp br0 on;
    brctl addif br0 eth1;
    brctl addif br0 eth2;
    (ifdown eth1 1>/dev/null 2>&1;);
    (ifdown eth2 1>/dev/null 2>&1;);
    ifconfig eth1 up;
    ifconfig eth2 up;
    ifconfig br0 up ### Adapt to your needs.
    brctl delif br0 eth1;
    brctl delif br0 eth2;
    ifconfig br0 down;
    brctl delbr br0;
    #ifup eth0; ### Adapt to your needs.
    #ifup eth1; ### Adapt to your needs.
    $0 stop;
    sleep 3;
    $0 start;

It resides in /etc/init.d and is called (imaginatively) and then has appropriate symlinks to rc2.d.

NTOP is reasonably easy to configure on Ubuntu and is quite straightforward to get going - point it at http://localhost:3000 and set your username/password and off you go.

A tip to remember is that in the /etc/default/ntop it's a good idea to uncomment GETOPT="" and change it to read (if your network was


and restart NTOP. Why is this important I hear you ask? Well on the br0 interface there is no IP assigned to it so NTOP doesn't automatically figure out what the local network is. By assigning this you can set it up to get proper info on local-remote, remote-remote and local-local traffic. Then leave it to run and see what it tells you.

Ah iftop is such a nice little bit of software. apt-get install it and then run it from the console with iftop -i br0 and it will tell you all sorts of things - data going from here to there and the level of bandwidth being used. I fancy pants it up a bit by creating a shell script and then launching it from there. iftop will use .iftoprc by default and if there isn't one will simply launch with it's own defaults. Here is the shell script I use (again I have adapted this from someone else):


# customisable settings
IFACE="br0" # the bridged interface

/usr/sbin/iftop -p -n -N -i $IFACE -F $LOCALNET -c $CONF

where /etc/iftoprc looks like this:

dns-resolution: yes
port-resolution: yes
show-bars: yes
promiscuous: no
port-display: source-only
#hide-source: yes
#hide-destination: yes
use-bytes: yes
sort: 2s
#line-display: one-line-both
show-totals: yes

Most of these are self-explanatory and I believe you should examine them more closely if you are looking to deploy it. Suffice to say, it gives me the info I want and I'm happy with that setup. So I hope that gives you some food for thought and you can take some of this away with you when you're trying to find out what the hell is chewing up all your bandwidth and download limit!


Popular posts from this blog

Plone - the open source Content Management System - a review

One of my clients, a non-profit, has a lot of files on it's clients. They need a way to digitally store these files, securely and with availability for certain people. They also need these files to expire and be deleted after a given length of time - usually about 7 years. These were the parameters I was given to search for a Document Management System (DMS) or more commonly a Content Management System (CMS). There are quite a lot of them, but most are designed for front facing information delivery - that is, to write something, put it up for review, have it reviewed and then published. We do not want this data published ever - and some CMS's make that a bit tricky to manage. So at the end of the day, I looked into several CMS systems that looked like they could be useful. The first one to be reviewed was OpenKM ( ). It looked OK, was open source which is preferable and seemed to have solid security and publishing options. Backing up the database and upgradin

Musings on System Administration

I was reading an article discussing forensic preparation for computer systems. Some of the stuff in there I knew the general theory of, but not the specifics of how to perform. As I thought about it, it occurred to me that Systems Administration is such a vast field. There is no way I can know all of this stuff. I made a list of the software and operating systems I currently manage. They include: - Windows Server 2003, Standard and Enterprise - Exchange 2003 - Windows XP - Windows Vista - Windows 2000 - Ubuntu Linux - OpenSuSE Linux - Mac OSX (10.3 and 10.4) - Solaris 8 - SQL 2005 - Various specialised software for the transport industry I have specific knowledge on some of this, broad knowledge on all of it, and always think "There's so much I *don't* know". It gets a bit down heartening sometimes. For one thing - I have no clue about SQL 2005 and I need to make it work with another bit of software. All complicated and nothing straightforward. Irritating doesn&

Traffic Monitoring using Ubuntu Linux, ntop, iftop and bridging

This is an update of an older post, as the utilities change, so has this concept of a cheap network spike - I use it to troubleshoot network issues, usually between a router and the network to understand what traffic is going where. The concept involves a transparent bridge between two network interface cards, and then looking at that traffic with a variety of tools to determine network traffic specifics. Most recently I used one to determine if a 4MB SDSL connection was saturated or not. It turned out the router was incorrectly configured and the connection had a maximum usage under 100Kb/s (!) At $1600 / month it's probably important to get this right - especially when the client was considering upgrading to a faster (and more expensive) link based on their DSL provider's advice. Hardware requirements: I'm using an old Dell Vostro desktop PC with a dual gigabit NIC in it - low profile and fits into the box nicely. Added a bit of extra RAM and a decent disk and that&