Computer and Information Security Handbook, 3rd Edition

Chapter e74

Firewalls

Errin W. Fulp     Wake Forest University, Winston-Salem, NC, United States

Abstract

The purpose of the firewall and its location is to have network connections traverse the firewall, which can then stop any unauthorized packets. A simple firewall will filter packets based on IP addresses and ports. A useful analogy is filtering your postal mail based only on the information on the envelope. You typically accept any letter addressed to you and return any letter addressed to someone else. This act of filtering is essentially the same for firewalls. This chapter refers to the secure network as the internal network; the insecure network is the external network. The remainder of this chapter provides an overview of firewall policies, ...