Byte.com: The Firewall Masquerade

“Whenever you connect to the Internet, you are establishing a
two-way connection between yourself and millions of other computer
users. No matter what type of computer you use, there are always
potential security holes in the operating system or application
code, configurations, etc., that might allow others to compromise
your data integrity. But when you implement a firewall, you make it
very difficult for anybody to hack into your system and crack

“A firewall gives you increased safety. In a car, for example,
the Firewall protects the occupants from the engine compartment. An
Internet Firewall protects the browsing computer(s) from prying
eyes on the network itself. It allows you to freely browse the
servers on the Internet while making it very difficult for anybody
to look back at your computer through the network connection.”

“Firewalls can be implemented with varying levels of security.
With Linux you can implement as much, or as little, security as you
need because there is a very wide range of firewall software
available. The most complex of these provide an almost impenetrable
level of security, but Linux also has a very simple technique
called ‘masquerading’ built right into the kernel itself that
offers a level of protection that is good enough to deter all but
the most concerted cracking attack.”