IPTables/NetFilter - Linux's Next-Generation Stateful Packet Filter
One of the goals of NetFilter was to provide a single, dedicated packet filter/mangler infrastructure that users and developers could deploy as an add-on built around the Linux kernel. For purposes of this article, packet filtering refers to the redirection of packets (but not modification of packet headers), while mangling refers to packet modification, typically of the source and/or destination IP address. NetFilter was designed to be modular and extensible. IPTables is a module that plugs into the NetFilter framework and allows the user access to kernel filtering/mangling rules and commands. If you are familiar with ipchains, you will notice the similarity between the syntax and format of IPTables and ipchains.
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