PF (Packet Filter, also written pf) is a

BSD license BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software. This is in contrast to copyleft licenses, which have share-alike requirements. The original BSD lic ...

d stateful

packet filter In computing, a firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted network and an untrusted ne ...

, a central piece of software for firewalling. It is comparable to

netfilter 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 addre ...

(

iptables iptables is a user-space utility program that allows a system administrator to configure the IP packet filter rules of the Linux kernel firewall, implemented as different Netfilter modules. The filters are organized in different tables, which ...

), ipfw, and ipfilter. PF was developed for

OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project em ...

, but has been

ported In software engineering, porting is the process of adapting software for the purpose of achieving some form of execution in a computing environment that is different from the one that a given program (meant for such execution) was originally desi ...

to many other

operating systems An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also inc ...

History

PF was originally designed as replacement for Darren Reed's IPFilter, from which it derives much of its rule syntax. IPFilter was removed from OpenBSD's CVS tree on 30 May 2001 due to OpenBSD developers' concerns with its license. The initial version of PF was written by Daniel Hartmeier. It appeared in OpenBSD 3.0, which was released on 1 December 2001. It was later extensively redesigned by Henning Brauer and Ryan McBride with most of the code written by Henning Brauer. Henning Brauer is currently the main developer of PF.

Features

The filtering syntax is similar to IPFilter, with some modifications to make it clearer. Network address translation (NAT) and

quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...

(QoS) have been integrated into PF. Features such as

pfsync pfsync is a computer protocol used to synchronise firewall states between machines running Packet Filter (PF) for high availability. It is used along with CARP to make sure a backup firewall has the same information as the main firewall. Wh ...

and

CARP Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...

for

failover Failover is switching to a redundant or standby computer server, system, hardware component or network upon the failure or abnormal termination of the previously active application, server, system, hardware component, or network in a computer net ...

and redundancy, authpf for session authentication, and ftp-proxy to ease firewalling the difficult

FTP The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and data ...

protocol, have also extended PF. Also PF supports SMP (

Symmetric multiprocessing Symmetric multiprocessing or shared-memory multiprocessing (SMP) involves a multiprocessor computer hardware and software architecture where two or more identical processors are connected to a single, shared main memory, have full access to all ...

) & STO (

Stateful Tracking Options In information technology and computer science, a system is described as stateful if it is designed to remember preceding events or user interactions; the remembered information is called the state of the system. The set of states a system can oc ...

). One of the many innovative features is PF's logging. PF's logging is configurable per rule within the pf.conf and logs are provided from PF by a pseudo-network interface called ''pflog'', which is the only way to lift data from kernel-level mode for user-level programs. Logs may be monitored using standard utilities such as

tcpdump tcpdump is a data-network packet analyzer computer program that runs under a command line interface. It allows the user to display TCP/IP and other packets being transmitted or received over a network to which the computer is attached. Distribut ...

, which in

has been extended especially for the purpose, or saved to disk in the

pcap In the field of computer network administration, pcap is an application programming interface (API) for capturing network traffic. While the name is an abbreviation of ''packet capture'', that is not the API's proper name. Unix-like systems ...

binary format using the ''pflogd'' daemon.

Ports

Apart from running on its home platform

, PF has been ported to many other operating systems, however there are major differences in capabilities. Some ports date back many years. OpenBSD always has the latest version with the most features. PF is currently used in: *

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

starting with version 5.3 * Apple

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

starting with ''Snow Leopard'' (Mac OS X 10.6) * Apple

iOS iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also includes ...

and

iPadOS iPadOS is a mobile operating system developed by Apple Inc. for its iPad line of tablet computers. It is a rebranded variant of iOS, the operating system used by Apple's iPhones, renamed to reflect the diverging features of the two product l ...

, used by all iPhones and iPads *

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is a ...

from version 3.0 *

DragonFly BSD DragonFly BSD is a free and open-source Unix-like operating system forked from FreeBSD 4.8. Matthew Dillon, an Amiga developer in the late 1980s and early 1990s and FreeBSD developer between 1994 and 2003, began working on DragonFly BSD in Ju ...

from version 1.1 *

Debian GNU/kFreeBSD Debian (), also known as Debian GNU/Linux, is a Linux distribution composed of free and open-source software, developed by the community-supported Debian Project, which was established by Ian Murdock on August 16, 1993. The first version of D ...

Oracle Solaris Solaris is a proprietary Unix operating system originally developed by Sun Microsystems. After the Sun acquisition by Oracle in 2010, it was renamed Oracle Solaris. Solaris superseded the company's earlier SunOS in 1993, and became known for it ...

QNX QNX ( or ) is a commercial Unix-like real-time operating system, aimed primarily at the embedded systems market. QNX was one of the first commercially successful microkernel operating systems. The product was originally developed in the early ...

and thereby in many BlackBerry smartphones models

References

Books

* * *

External links