Testing Your Linux Firewall Effectively with FTester Utility

Recently, I wrote an article about "How to scan your Linux-Distro for Root Kits". Now that the machine is... clean! I think, a good thing TO-DO, is to test my Firewall (AGAIN!) The good news are that we can use the free tool FTester. The bad news are that FTester needs to be configured right...So...Let's get to work!

The tool consists of two perl scripts, a packet injector (ftest) and the listening sniffer (ftestd). The first script injects custom packets, defined in ftest.conf, with a signature in the data part while the sniffer listens for such marked packets. The scripts both write a log file which is in the same form for both scripts. A diff of the two produced files (ftest.log and ftestd.log) shows the packets that were unable to reach the sniffer due to filtering rules if these two scripts are ran on hosts placed on two different sides of a firewall. Stateful inspection firewalls are handled with the 'connection spoofing' option. A script called freport is also available for automatically parse the log files.

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