Introduction

Firewalls are used to protect private networks from being attacked by external network users. Typically, the external network user is located on the Internet. However, any user located on an untrusted network should be considered a potential threat to the corporate network.

Companies use firewalls to control what types of packets are allowed into, and out of, the confines of the corporate network. Any packets that do not match an approved packet type are dropped by the firewall. The firewall administrator determines in advance what packets are allowed into and out of the corporate network.

In this chapter, we examine the role firewalls play in protecting the private network from attack by external network hosts. By the time you finish this chapter, you will be able to assess what type of firewall solution best fits your security requirements and understand how the firewall works in carrying out your security policies.