Firewall

Introduction

        Information systems in corporations, government agencies and other organizations have undergone a steady evolution:
    • Centralized data processing systems, with a central mainframe supporting a number of directly connected terminals.
    • Local Area networks (LANs) interconnecting PCs and terminals to each other and the mainframe.
    • Premises network, consisting of a number of LANs, interconnecting PCs servers, and perhaps a mainframe or two.
    • Enterprises wide network, consisting of multiple, geographically distributes premises networks interconnects by a private wide area networks (WAN).
        Interconnectivity is no longer an option for most organizations. The information and services available are essential to the organizations. Moreover, individual users within the organization want and need Internet access, and if this is not provided via LAN, they will use dial-up capability from their PC to an Internet service provider (ISP). However, while Internet access provides benefits to the organization, it enables the outside world to reach and interact with local network assets. This creates a threat to the organization. While it is possible to equip each workstation and server in the premises network with strong security features, such as intrusion protection, this is not a practical approach. Consider a network with hundreds or even thousands of systems, running a mix of various versions of UNIX, plus Windows. When a security flaw is discovered, each potentially affected system must be upgraded to fix this flaw. The alternative, increasingly accepted, is the firewall. The firewall is inserted between the premises network and the Internet to establish a controlled link and to erect an outer security wall or perimeter. The aim of this perimeter is to protect the premises network from Internet-based attacks and to provide a single choke point where security and audit can be imposed. The firewall may be a single computer... [continues]

Read full essay