SecurityFocus has released a new paper called Linux Firewall-related /proc Entries.

Here is an excerpt:

Most people, when creating a Linux firewall, concentrate soley on manipulating kernel network filters: the rulesets you create using userspace tools such as iptables (2.4 kernels,) ipchains (2.2 kernels,) or even ipfwadm (2.0 kernels).

However there are kernel variables -- independent of any kernel filtering rules -- that affect how the kernel handles network packets. This article will discuss these variables and the effect they have on the network security of your Linux host or firewall.
To read the full article click here: Linux Firewall-related /proc Entries