The
iptables firewall feature is included with every Linux distribution that comes
with this book.
ON the CD-ROM
467
IN THIS CHAPTER
Understanding firewalls
Protecting desktops with
firewalls
Managing firewalls with iptables
Making a Coyote Linux bootable
firewall floppy
Getting other bootable firewalls
Running a Linux
Firewall/Router
Understanding Firewalls
A firewall refers to hardware or software tools that limit access to a computer or network based on a
defined security policy. As used in this chapter, firewall refers to a piece of software that examines
every network packet coming from the Internet to decide whether it should be allowed in, rejected
completely, ignored, or modified. Every recent Linux system has firewall features available because
they are built into the Linux kernel in a facility called iptables. But firewalls in Linux can be used
differently, depending on what you are doing with your Linux system:
Desktop system??”A Linux system used only to run applications and browse the Web
may simply use its firewall to block all (or nearly all) incoming requests for services. By
doing so, the only data that can come into the desktop system is in response to requests
initiated by that computer itself. When that desktop itself is behind a corporate firewall,
firewall rules can often be relaxed to allow various kinds of file and printer sharing to
take place behind that firewall.
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