Netfilter
packet alteration framework for Linux and the umbrella project for software of the same
Netfilter is a framework provided by the Linux kernel that allows various networking-related operations to be implemented in the form of customized handlers. Netfilter offers various functions and operations for packet filtering, network address translation, and port translation, which provide the functionality required for directing packets through a network and prohibiting packets from reaching sensitive locations within a network.
Netfilter represents a set of hooks inside the Linux kernel, allowing specific kernel modules to register callback functions with the kernel's networking stack. Those functions, usually applied to the traffic in the form of filtering and modification rules, are called for every packet that traverses the respective hook within the networking stack.
History
Rusty Russell started the netfilter/iptables project in 1998; he had also authored the project's predecessor, ipchains. As the project grew, he founded the Netfilter Core Team (or simply coreteam) in 1999. The software they produced (called netfilter hereafter) uses the GNU General Public License (GPL) license, and on 26 August 1999 it was merged into version 2.3.15 of the Linux kernel mainline and thus was in the 2.4.0 stable version.
In August 2003 Harald Welte became chairman of the coreteam. In April 2004, following a crack-down by the project on those distributing the project's software embedded in routers without complying with the GPL, a German court granted Welte an historic injunction against Sitecom Germany, which refused to follow the GPL's terms (see GPL-related disputes). In September 2007 Patrick McHardy, who led development for past years, was elected as new chairman of the coreteam.
The public source identifies “Netfilter” as packet alteration framework for Linux and the umbrella project for software of the same. This brief keeps that definition visible, then builds a research path around Netfilter, packet and alteration.
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This entry incorporates text from “Netfilter” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.