Chapter 31 Firewalls

Table of Contents
31.1 Introduction
31.2 Firewall Concepts
31.3 Firewall Packages
31.4 PF and ALTQ
31.5 The IPFILTER (IPF) Firewall
31.6 IPFW
Contributed by Joseph J. Barbish. Converted to SGML and updated by Brad Davis.

31.1 Introduction

Firewalls make it possible to filter the incoming and outgoing traffic that flows through a system. A firewall can use one or more sets of “rules” to inspect network packets as they come in or go out of network connections and either allows the traffic through or blocks it. The rules of a firewall can inspect one or more characteristics of the packets such as the protocol type, source or destination host address, and source or destination port.

Firewalls can enhance the security of a host or a network. They can be used to do one or more of the following:

After reading this chapter, you will know:

Before reading this chapter, you should: