IPTABLES
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iptables & netfilter - How to get started

Information about Linux' build-in firewall

 

Netfilter is the set of hooks within the Linux kernel for intercepting and manipulating network packets. The best-known component on top of netfilter is the firewall which filters packets, but the hooks are also used by a component which performs network address translation, and by another which provides ipchains backwards compatibility. [...]

iptables is the name of the user space tool by which administrators create rules for the packet filtering and NAT modules. While technically iptables is merely the tool which controls the packet filtering and NAT components within the kernel, the name iptables is often used to refer to the entire infrastructure, including netfilter, connection tracking and NAT, as well as the tool itself.” (from Wikipedia)

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