Firewalls
...policy between two or more networks. The means by which this control is accomplished varies widely, but in principle, the firewall is a pair of mechanisms, one that blocks traffic and one that permits traffic. Some firewalls emphasize blocking traffic, while others emphasize permitting traffic. The most important thing to recognize about a firewall is that it implements an access control policy. If you don't know what kind of access you want to permit or deny, or you let someone else or some product configure a firewall based on judgment other than yours, that entity is making policy for your whole organization.
WHY WOULD I WANT A FIREWALL?
The Internet is a fun little playground and at the same time a hostile environment. Like any other society, it's plagued with the kind of people who enjoy the electronic equivalent of writing on other people's walls with spray paint, tearing off their mailboxes, or just sitting in the street blowing their car horns. Some people get real work done over the Internet, and some must protect sensitive or proprietary data. Usually, a firewall's purpose is to keep the intruders out of your network while letting you do your job.
Many traditional corporations and data centers have computing security policies and practices that users must follow. If a company's policies dictate how data must be protected, a firewall is very important because it embodies corporate policy. Frequently, the hardest part of hooking a large company to the Internet is not justifying the expense or effort, but instead convincing management that it's safe to do so. A firewall not only provides real security but also plays an important role as a security blanket for management.
Last, a firewall can act as your corporate ambassador to the Internet. Many corporations use their firewall systems to store public information about corporate products and services,...
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