Implementation of data collection tools using NetFlow for statistical ...

4 Implementation
Verifying the NetFlow-data
Once the router configuration of sending NetFlow-data to the Linux machine was completed, it had
to be verified that the computer actually got the flow-data. This was done by using a terminal-based
version of the popular packet analyzer Wireshark named TShark [52].
The following syntax was used in order to make TShark focus on port 2100, the default port for
NetFlow-data and save the results to a file:
tshark -ni eth0 -R udp.port==2100 -d udp.port==2100,cflow -V >
tshark.cap
The file rapidly grew in size and after viewing the contents it was concluded that the router was
correctly configured to send NetFlow-data to the computer. Below are two excerpts from the
captured traffic, each displaying the duration of the flow and other relevant information.
Illustration 8: Captured flow between two
parties
Quagga
Illustration 7: Traffic destined for port 80,
HTTP
Configuring Quagga to exchange neighbor traffic with the small router turned out to be very easy
and was done fairly quickly. It turned out to be Quagga that had the solution to avoid disrupting
customer traffic by a wrongful configuration; in order to disrupt the customer traffic, it would have
been mandatory that Quagga be configured with networks it could advertise as its own to other
routers. If the same network(s) also existed on the real router, it would cause an interruption in
traffic as both routers would claim ownership over the same networks. It is possible, however
unlikely, that this new information would be propagated further out on the Internet as well. ISP's are
generally very careful with advertising networks and usually have some sort of filter to only allow
routing updates containing their own networks to be sent out. Since Quagga did not have any
networks it could advertise to other router(s), wrongful configuration could not occur as it only
listened to routing updates; it never sent any of its own. It was also one of the things that “just
worked” and did not need any special attention once it was set up.
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