3. Build a kernel with IPCHAINS Firewall support

The first thing you need to do is ensure that your kernel has been built with Network Firewall support enabled and Firewalling. Remember, all servers should be configured to block unused ports, even if there are no firewall server. In the 2.2.14 kernel version you need to be sure that you have answered Y to the following questions:

          Networking options:
          Network firewalls (CONFIG_FIREFALL) [N] Y
          IP:Firewalling (CONFIG_IP_FIREWALL) [N] Y
          IP:TCP syncookie support (CONFIG_SYN_COOKIES) [N] Y

If you have followed the Linux Kernel section and have recompiled your kernel, the options Network firewalls, IP:Firewalling, and IP:TCP syncookie support shown above are already set.