Linux Firewalls

Default iptables Policy

We now have a functioning Linux system with iptables installed. The remainder of this chapter will concentrate on various administrative and run-time aspects of iptables firewalls.

We'll begin by constructing a Bourne shell script (iptables.sh) to implement an iptables filtering policy tailored for a modest network with a permanent Internet connection. This policy will be used throughout the rest of the book and serves as a common ground—we will refer to this policy in several subsequent chapters. You can also download the iptables.sh script from http://www.cipherdyne.org/linuxfirewalls. But first, here is some background information on iptables.

Policy Requirements

Let's define the requirements for an effective firewall configuration ...