Note: This article was inspired by the lack of updated documentation on how to write proper netfilter kernel modules. At the time I’m writing this article, the latest stable release was 2.6.32.8. I am also assuming you are familiar with how LKMs (Loadable Kernel Modules) work. If you are not, then you might want to check this article first: tldp.org/HOWTO/Module-HOWTO/

In this article (Part 1) I will present how to create a simple Linux kernel module that implements a netfilter hook for a generic transport protocol (not one of the usual ones).

In Part 2, I plan to connect the module to the iptables rules generated on the userspace side.
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