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 ( 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 script from But first, here is some background information on iptables.

Policy Requirements

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

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