Application firewall

An application firewall is a form of firewall that controls input/output or system calls of an application or service. It operates by monitoring and blocking communications based on a configured policy, generally with predefined rule sets to choose from. The application firewall can control communications up to the application layer of the OSI model, which is the highest operating layer, and where it gets its name. The two primary categories of application firewalls are network-based and host-based. Gene Spafford of Purdue University, Bill Cheswick at AT&T Laboratories, and Marcus Ranum described a third-generation firewall known as an application layer firewall. Marcus Ranum's work, based on the firewall created by Paul Vixie, Brian Reid, and Jeff Mogul, spearheaded the creation of the first commercial product. The product was released by DEC, named the DEC SEAL by Geoff Mulligan - Secure External Access Link. DEC's first major sale was on June 13, 1991, to Dupont. Under a broader DARPA contract at TIS, Marcus Ranum, Wei Xu, and Peter Churchyard developed the Firewall Toolkit (FWTK) and made it freely available under license in October 1993. The purposes for releasing the freely available, not for commercial use, FWTK were: to demonstrate, via the software, documentation, and methods used, how a company with (at the time) 11 years experience in formal security methods, and individuals with firewall experience, developed firewall software; to create a common base of very good firewall software for others to build on (so people did not have to continue to "roll their own" from scratch); to "raise the bar" of firewall software being used. However, FWTK was a basic application proxy requiring the user interactions. In 1994, Wei Xu extended the FWTK with the Kernel enhancement of IP stateful filter and socket transparent. This was the first transparent firewall, known as the inception of the third generation firewall, beyond a traditional application proxy (the second generation firewall), released as the commercial product known as Gauntlet firewall.