If you want your Linux-Box to do firewalling you must first ensure that your kernel has been compiled with the relevant options turned on If you needed assistance howto configure, compile and install a new kernel, refer back to chapter VIII of the LinuxFromScratch book, Installing a kernel and eventually Making the LFS system bootable ; note, that you'll need to reboot to actually run your new kernel.. How to configure your kernel, with enabling the options to be either compiled into the kernel or as modules, depends on your personal preferences and experience. Note, that for the quoted scripts it is assumed that the modules need to be loaded at first. Networking options: Network packet filtering = CONFIG_NETFILTER Unix domain sockets = CONFIG_UNIX IP: TCP/IP networking = CONFIG_INET IP: advanced router = CONFIG_IP_ADVANCED_ROUTER IP: verbose route monitoring = CONFIG_IP_ROUTE_VERBOSE IP: TCP Explicit Congestion Notification support = CONFIG_INET_ECN IP: TCP syncookie support = CONFIG_SYN_COOKIES IP: Netfilter Configuration: every option = CONFIG_IP_NF_* WITHOUT: ipchains (2.2-style) support ipfw-adm (2.0-style) support w\ CONFIG_IP_NF_COMPAT_* Fast switching Make sure to disable it because it would setup a bypass around your firewalling-rules. w\ CONFIG_NET_FASTROUTE