Any free solution for DI (Deep Inspection) firewall or routers available for Linux? Are there any plans for DI focus functions appear to the future IPTABLES? I know there are tools for most prevalent static internet protocol such as HTTP, SMTP, IMAP, POP, FTP, and DNS, but we live in a time, we need to go beyond them. I know there are products like Procera and Ellacoya, but there must be a free and open source solution to this problem, so things can be deployed faster based on the tech knowledge, not deep pockets.

A full-on firewall (or router), no, you're not going to find many and those that claim to do this are most likely selling snake oil, IMO. A firewall should permit or deny traffic based on things other than deep packet inspection. To have a firewall do things other than what a basic firewall is intended to do (free or commercial) is just asking for trouble. As it is, at work we always seem to have issues with the IPS/IDP platforms. They either die when updating policies or seize because something within a packet's payload clogs/blocks the system, sending CPU cycles to 100%. IMO, if an IPS has issues assessing packets at a deep level, a firewall is going to have similar issues. Even if there's nothing within packets that will seize or kill the inspection, can you imagine the load of CPU cycles that a busy perimeter firewall would have conducting deep packet inspection of every packet?? The load would be huge, even on a multiproc or multicore system...the load may be big enough to where the system would slow, fail, or begin dropping packets.

An IPS MAY do what you'd like, though. One free solution is snort-inline, I believe.

What exactly are you trying to accomplish? Yes I have skimmed this article, but I don’t know exactly what you are seeking.

Will a concept as simple as l7-filter (with very complicated pattern definitions) be sufficient?