5 - Protecting Your Intranet from the Extranet and Internet

Abstract

A firewall is a system designed to control access to applications on a network, typically access to a private network from the public Internet. There are many different choices when it comes to defining the topology, selecting the vendor, and selecting the type of firewall—operating system (OS) security, application security, and solid policies and procedures—although they are not a 100% guarantee. The question is to determine how much security is needed. The main function of a firewall is to protect the internal proprietary data from the outside world. There are three major types of firewalls used for protecting an enterprise's Intranet—packet filtering, proxy server or application gateway, and circuit-level gateway or generic application proxy—but any device that controls traffic flowing through a network for security reasons can be considered a firewall. The three major types of firewalls utilize different methods to accomplish the same thing—protect an internal network. The most basic type of firewall is a packet-filtering device, also known as a screening router. Packet filtering firewalls are routers that operate in the low levels of a network protocol stack.