William Fithen
Julia Allen
Ed Stoner
Security Improvement Module
CMU/SEI-SIM-008
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A firewall is a combination of hardware and software used to implement a
security policy governing the network traffic between two or more networks,
some of which may be under your administrative control (e.g., your
organizations networks) and some of which may be out of your control (e.g.,
the Internet). A network firewall commonly serves as a primary line of defense
against external threats to your organization's computer systems, networks,
and critical information. Firewalls can also be used to partition your
organizations internal networks, reducing your risk from insider attacks.
Firewall technologies have entered into the mainstream. The [Power 99]
indicates that 91 percent of the organizations surveyed already deploy
firewalls. Articles and other references covering evaluation, selection, and
configuration of firewall technologies are now common in the popular press
(see References at the end of this section). However, there has been little
published about designing, installing, deploying, operating, and maintaining
firewalls. The practices in this module will address designing, installing,
and deploying firewalls.
The term firewall is taken from the structural analog whose purpose is to
slow the spread of fire in a building. In the computer literature, popular
press, and vendor marketing materials, the term is used in many ways. Some
people use it to identify a specific hardware component or software package,
while others consider the entire collection of systems and software deployed
between two networks to be parts of a firewall.
Throughout these practices, we will generally use the term firewall as an
adjective modifying a noun (such as system, hardware, software, product) to
make the reference clear. When we use the term firewall as a noun, we mean the
general concept of a technological mechanism for the enforcement of a network
traffic security policy. While this may seem cumbersome at times, we believe
these distinctions will increase your understanding of our intent.
