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Linux Firewalls by Michael Rash

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Packet Filtering with iptables

The iptables firewall allows the user to instrument a high degree of control over IP packets that interact with a Linux system; that control is implemented within the Linux kernel. A policy can be constructed with iptables that acts as a vigorous traffic cop—packets that are not permitted to pass fall into oblivion and are never heard from again, whereas packets that pass muster are sent on their merry way or altered so that they conform to local network requirements.

An iptables policy is built from an ordered set of rules, which describe to the kernel the actions that should be taken against certain classes of packets. Each iptables rule is applied to a chain within a table. An iptables chain is a collection of ...

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