Chapter 30 Firewalls

Table of Contents
30.1 Introduction
30.2 Firewall Concepts
30.3 Firewall Packages
30.4 The OpenBSD Packet Filter (PF) and ALTQ
30.5 The IPFILTER (IPF) Firewall
30.6 IPFW
Contributed by Joseph J. Barbish. Converted to SGML and updated by Brad Davis.

30.1 Introduction

Firewalls make it possible to filter incoming and outgoing traffic that flows through your system. A firewall can use one or more sets of “rules” to inspect the network packets as they come in or go out of your 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, including but not limited to the protocol type, the source or destination host address, and the source or destination port.

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

After reading this chapter, you will know:

Before reading this chapter, you should:

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