Wireless Mobile Internet Security, 2nd Edition

Chapter 11

Internet Firewalls for Trusted Systems

A firewall is a device or group of devices that controls access between networks. A firewall generally consists of filters and gateway(s), varying from firewall to firewall. It is a security gateway that controls access between the public Internet and an intranet (a private internal network) and is a secure computer system placed between a trusted network and an untrusted Internet. A firewall is an agent that screens network traffic in some way, blocking traffic it believes to be inappropriate, dangerous, or both. The security concerns that inevitably arise between the sometimes hostile Internet and secure intranets are often dealt with by inserting one or more firewalls in the path connecting the Internet and the internal network. In reality, Internet access provides benefits to individual users, government agencies, and most organizations. But this access often creates a threat as a security flaw. The protective device that has been widely accepted is the firewall. When inserted between the private intranet and the public Internet, it establishes a controlled link and erects an outer security wall or perimeter. The aim of this wall is to protect the intranet from Internet-based attacks and to provide a choke point where security can be imposed.

Firewalls act as an intermediate server in handling SMTP and HTTP connections in either direction. Firewalls also require the use of an access negotiation and encapsulation protocol such ...