In computing, a stateful firewall is a network-based firewall that individually tracks sessions of network connections traversing it. Stateful packet inspection, also referred to as dynamic packet filtering, is a security feature often used in non-commercial and business networks.
Unix security refers to the means of securing a Unix or Unix-like operating system. A secure environment is achieved not only by the design concepts of these operating systems, but also through vigilant user and administrative practices.
PF is a BSD licensed stateful packet filter, a central piece of software for firewalling. It is comparable to netfilter (iptables), ipfw, and ipfilter.
In computer networking, port forwarding or port mapping is an application of network address translation (NAT) that redirects a communication request from one address and port number combination to another while the packets are traversing a network gateway, such as a router or firewall. This technique is most commonly used to make services on a host residing on a protected or masqueraded (internal) network available to hosts on the opposite side of the gateway, by remapping the destination IP address and port number of the communication to an internal host.
IPFilter is an open-source software package that provides firewall services and network address translation (NAT) for many Unix-like operating systems. The author and software maintainer is Darren Reed. IPFilter supports both IPv4 and IPv6 protocols, and is a stateful firewall.
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.
Shorewall is an open source firewall tool for Linux that builds upon the Netfilter (iptables/ipchains) system built into the Linux kernel, making it easier to manage more complex configuration schemes by providing a higher level of abstraction for describing rules using text files. Its documentation is hosted on shorewall.org, while the latest code is hosted at https://gitlab.com/shorewall/code.
FireHOL is a shell script designed as a wrapper for iptables written to ease the customization of the Linux kernel's firewall netfilter. FireHOL is free software and open-source, distributed under the terms of the GNU General Public License.
Linux IP Firewalling Chains, normally called ipchains, is free software to control the packet filter or firewall capabilities in the 2.2 series of Linux kernels. It superseded ipfirewall, but was replaced by iptables in the 2.4 series. Unlike iptables, ipchains is stateless.
Firestarter is a personal firewall tool that uses the Netfilter (iptables/ipchains) system built into the Linux kernel. It has the ability to control both inbound and outbound connections. Firestarter provides a graphical interface for configuring firewall rules and settings. It provides real-time monitoring of all network traffic for the system. Firestarter also provides facilities for port forwarding, internet connection sharing and DHCP service.
libipq is a development library for iptables userspace packet queuing. Libipq provides an API for communicating with ip_queue.
ipfirewall or ipfw is a FreeBSD IP, stateful firewall, packet filter and traffic accounting facility. Its ruleset logic is similar to many other packet filters except IPFilter. ipfw is authored and maintained by FreeBSD volunteer staff members. Its syntax enables use of sophisticated filtering capabilities and thus enables users to satisfy advanced requirements. It can either be used as a loadable kernel module or incorporated into the kernel; use as a loadable kernel module where possible is highly recommended. ipfw was the built-in firewall of Mac OS X until Mac OS X 10.7 Lion in 2011 when it was replaced with the OpenBSD project's PF. Like FreeBSD, ipfw is open source. It is used in many FreeBSD-based firewall products, including m0n0wall and FreeNAS. A port of an early version of ipfw was used since Linux 1.1 as the first implementation of firewall available for Linux, until it was replaced by ipchains. A modern port of ipfw and the dummynet traffic shaper is available for Linux and Microsoft Windows. wipfw is a Windows port of an old (2001) version of ipfw.
Rope is a programming language that allows developers to write extensions to the Iptables/Netfilter components of Linux using a simple scripting language based on Reverse Polish notation.
Netlink is a socket family used for inter-process communication (IPC) between both the kernel and userspace processes, and between different userspace processes, in a way similar to the Unix domain sockets available on certain Unix-like operating systems, including its original incarnation as a Linux kernel interface, as well as in the form of a later implementation on FreeBSD. Similarly to the Unix domain sockets, and unlike INET sockets, Netlink communication cannot traverse host boundaries. However, while the Unix domain sockets use the file system namespace, Netlink sockets are usually addressed by process identifiers (PIDs).
NuFW is a software package that extends Netfilter, the Linux kernel-internal packet filtering firewall module. NuFW adds authentication to filtering rules. NuFW is also provided as a hardware firewall, in the EdenWall firewalling appliance. NuFW has been restarted by the FFI and renamed into UFWI.
An application-level gateway is a security component that augments a firewall or NAT employed in a computer network. It allows customized NAT traversal filters to be plugged into the gateway to support address and port translation for certain application layer "control/data" protocols such as FTP, BitTorrent, SIP, RTSP, file transfer in IM applications. In order for these protocols to work through NAT or a firewall, either the application has to know about an address/port number combination that allows incoming packets, or the NAT has to monitor the control traffic and open up port mappings dynamically as required. Legitimate application data can thus be passed through the security checks of the firewall or NAT that would have otherwise restricted the traffic for not meeting its limited filter criteria.
Fail2ban is an intrusion prevention software framework. Written in the Python programming language, it is designed to prevent brute-force attacks. It is able to run on POSIX systems that have an interface to a packet-control system or firewall installed locally, such as iptables or TCP Wrapper.
The arptables computer software utility is a network administrator's tool for maintaining the Address Resolution Protocol (ARP) packet filter rules in the Linux kernel firewall modules.
nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames. It has been available since Linux kernel 3.13 released on 19 January 2014.
firewalld is a firewall management tool for Linux operating systems. It provides firewall features by acting as a front-end for the Linux kernel's netfilter framework. firewalld's current default backend is nftables. Prior to v0.6.0, iptables was the default backend. Through its abstractions, firewalld acts as an alternative to nft and iptables command line programs. The name firewalld adheres to the Unix convention of naming system daemons by appending the letter "d".
