# IPFilter

> free packet filtering and NAT software

**Wikidata**: [Q1654315](https://www.wikidata.org/wiki/Q1654315)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/IPFilter)  
**Source**: https://4ort.xyz/entity/ipfilter

## Summary
IPFilter is a free packet filtering and NAT software that functions as a stateful firewall for Unix-like operating systems. It provides network security through connection tracking and packet filtering capabilities.

## Key Facts
- IPFilter is licensed under both the GNU General Public License and BSD licenses
- The software runs on Unix-like operating systems and requires this operating system to function
- Version 1.0 was released on April 22, 1993, with subsequent versions including 2.0 (December 18, 1994), 2.8 (September 15, 1995), 3.4 (April 27, 2000), 4.1.30 (July 24, 2008), 4.1.33 (August 16, 2009), and 5.1.0/5.1.2
- The project is hosted on SourceForge under the project name "ipfilter"
- IPFilter has been replaced by OpenBSD PF in some implementations
- The software has Wikipedia articles in 9 languages including English, German, French, Russian, and Chinese

## FAQs
### Q: What is IPFilter used for?
A: IPFilter is used for packet filtering and Network Address Translation (NAT) on Unix-like operating systems. It functions as a stateful firewall that tracks network connections and filters network traffic based on configurable rules.

### Q: Is IPFilter free software?
A: Yes, IPFilter is free software distributed under dual licensing - both the GNU General Public License and BSD licenses. This allows users to freely use, modify, and distribute the software.

### Q: What operating systems support IPFilter?
A: IPFilter runs on Unix-like operating systems, which are operating systems that behave in a manner similar to Unix systems. This includes various Linux distributions, BSD variants, and other Unix-compatible systems.

## Why It Matters
IPFilter represents an important contribution to network security infrastructure by providing a free, open-source solution for packet filtering and NAT functionality. As a stateful firewall, it helps organizations and individuals protect their networks by tracking active connections and making decisions about which network packets to allow or block. The software's long development history, spanning from 1993 to the present, demonstrates its reliability and the ongoing need for such network security tools. IPFilter's dual licensing under both GPL and BSD licenses made it accessible to a wide range of users and contributed to the broader ecosystem of free network security software. Its replacement by OpenBSD PF in some contexts also illustrates the natural evolution of open-source security tools as communities develop and improve upon existing solutions.

## Notable For
- Being one of the earlier free software solutions for packet filtering and NAT on Unix-like systems
- Maintaining a long development history from 1993 to present with multiple stable versions
- Offering dual licensing under both GPL and BSD licenses, providing flexibility for different use cases
- Supporting multiple programming languages and having an active mailing list for community support
- Being replaced by OpenBSD PF in some implementations, showing its influence on subsequent firewall development

## Body
### Development History
IPFilter was first released on April 22, 1993, as version 1.0. The software has undergone numerous updates and improvements over the years, with major versions including 2.0 (December 18, 1994), 2.8 (September 15, 1995), 3.4 (April 27, 2000), and the 4.x series culminating in 4.1.33 (August 16, 2009). The 5.x series includes versions 5.1.0 and 5.1.2.

### Technical Architecture
As a stateful firewall, IPFilter maintains information about active network connections and uses this context to make more intelligent filtering decisions compared to simple packet filters. The software implements Network Address Translation (NAT), allowing multiple devices on a local network to share a single public IP address.

### Licensing and Distribution
IPFilter is distributed under dual licensing - both the GNU General Public License and BSD licenses. This dual licensing approach provides users with flexibility in how they can use and distribute the software. The project is hosted on SourceForge, a popular platform for open-source software development.

### Community and Support
The IPFilter project maintains an active mailing list archive accessible at marc.theaimsgroup.com, providing a platform for users to discuss issues, share configurations, and get support. The software's Wikipedia presence in 9 different languages indicates its international user base and community support.

### Relationship to Other Software
IPFilter has been replaced by OpenBSD PF (Packet Filter) in some implementations, particularly in OpenBSD systems. This transition represents the natural evolution of firewall technology and the open-source community's ongoing efforts to improve network security tools.

## References

1. [Source](https://web.archive.org/web/2013/doc.m0n0.ch/handbook/apas05.html)
2. [Source](https://sourceforge.net/projects/ipfilter/#reviews)
3. [Source](https://master.dl.sourceforge.net/project/ipfilter/ipfilter/ip_fil4.1.33.tar.gz?viasf=1#HISTORY)
4. Freebase Data Dumps. 2013
5. [Source](https://web.archive.org/web/2020/phildev.net/ipf/IPFmail.html#mail5)