L7-filter

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L7-filter is a classifier for Linux's Netfilter subsystem that identifies packets based on application layer data. The major goal of this is to make possible the identification of peer to peer programs, which use unpredictable port numbers. It is implemented as a kernel module in Linux 2.4 and 2.6. An experimental version was released in December 2006 which runs as a user-space program.

L7-filter uses regular expressions to identify the protocol that generates or consumes each packet. This technique, used in conjunction with a QoS system, allows port-independent traffic shaping.

It seems that l7-filter has problems handling recent kernel's (2.6.20/21) netfilter implementation.

All versions of l7-filter have been released under the GNU General Public License.