Firewall

A firewall is a network security system that monitors and controls incoming and outgoing network traffic according to a set of configured rules, establishing a boundary between a trusted network and an untrusted one such as the public Internet. Engineers at Digital Equipment Corporation built the earliest documented packet-filtering firewall technology in 1987, and William Cheswick and Steven Bellovin at AT&T Bell Labs built a working packet-filtering system of their own soon after; Bell Labs colleagues Dave Presotto, Janardan Sharma and Kshitij Nigam then developed circuit-level gateways between 1989 and 1990, letting a firewall track entire conversations between two network endpoints rather than inspecting packets in isolation. Marcus Ranum, Wei Xu and Peter Churchyard released the Firewall Toolkit in October 1993, the basis of the commercial Gauntlet firewall, and the PIX Firewall, built by the consultant Brantley Coile for Network Translation Inc. in 1994, became a commercial success after Cisco Systems acquired the company in November 1995.