2 posts earlier, I talked about NetFlow in VMware 5.x and how to enable it in vSphere dvSwitch. I have also shown how you can send IP traffic flow information to a NetFlow collector. Nowadays, there are lots of commercial NetFlow collectors available; however, in this post I will introduce a simple, open-source NetFlow collector which you can use in your VMware environment to analyze IP traffic. This pretty piece of software is: ‘nfdump‘

As it’s shown, Nfdump has 2 major elements: ‘nfcapd‘ which is a daemon to gather and store relevant packets and ‘nfdump‘ which collects packets from all the daemons and interprets them. Apparently, nfcapd and nfdump could run on different machines and there could be multiple daemons but in case of VMware vSphere, it depends solely on the number of dvSwitches. If there is only one distributed switch, all the IP traffic flow information from all portgroups in that dvSwitch will be forwarded to one nfcapd. For test purposes, I also deployed both nfdump and nfcapd on a single linux machine but in cases that traffic is high, it maybe a good idea to deploy them on two different machines. Of course nfdump should have access to the storage in that case.

After installation, first you need to run daemon and specify a port and directory to store ip traffic information. Apparently, nfcapd will store information in binary. The command is simple, something like this:

• nfcapd -w -D -l /var/netflow/dvswitch -p 23456

Then, daemon will run and listen to the specified port: 23456. If you have configured dvSwitch correctly (by specifying ip address of linux machine and 23456 as port) and activated monitoring on some portgroups in vCenter, this daemon will generate a couple of files in that directory.
Now, whenever you want to view the captured ip traffic flows, you should run nfdump. Since there are lots of files in that directory, you can interpret the whole directory using -R option with this command:

• nfdump -R /var/netflow/dvswitch/

Filtering in nfdump is also possible, pretty much the same as tcpdump and you can view traffics of interest. You can find more information on nfdump website.

To view NetFlow captured traffic visually, you can mix nfsen with nfdump. It uses information that is dumped by daemon and utilizing rrdtool, it visualizes traffic flow. Installation is not difficult and you can see more information on their website. I’m really satisfied by this beautiful combination of nfdump and nfsen and if you intend to use NetFlow for monitoring, I recommend trying them. Good Luck!