Some of you might be familiar with the netflow protocol, but if you are not, it is quite simple. Basically a device capable of netflow collects all IP traffic and sends the data to a server to analyze it further, allowing the administrator to see where the traffic is coming from and where it is going. But you might want to read up on this topic on wikipedia.
Now the IPFire system does not out of the box offer support for the netflow protocol but thanks to the really awesome addon system it is very simple to extend its functionality. Since there was no addon that allowed me to install a netflow probe I went ahead and created a fprobe package for ipfire. I went with fprobe because all the requirements were already met on the ipfire system and it is quite lightweight on system resources.