P-660HW-Dx User’s Guide 143
CHAPTER 9 Firewalls
This chapter gives some background information on firewalls and introduces the ZyXEL
Device firewall.
9.1 Firewall Overview
Originally, the term firewall referred to a construction technique designed to prevent the
spread of fire from one room to another. The networking term “firewall” is a system or group
of systems that enforces an access-control policy between two networks. It may also be
defined as a mechanism used to protect a trusted network from an untrusted network. Of
course, firewalls cannot solve every security problem. A firewall is one of the mechanisms
used to establish a network security perimeter in support of a network security policy. It
should never be the only mechanism or method employed. For a firewall to guard effectively,
you must design and deploy it appropriately. This requires integrating the firewall into a broad
information-security policy. In addition, specific policies must be implemented within the
firewall itself.
Refer to Section 10.5 on page 158 to configure default firewall settings.
Refer to Section 10.6 on page 159 to view firewall rules.
Refer to Section 10.6.1 on page 161 to configure firewall rules.
Refer to Section 10.6.2 on page 164 to configure a custom service.
Refer to Section 10.10.3 on page 173 to configure firewall thresholds.
9.2 Types of Firewalls
There are three main types of firewalls:
• Packet Filtering Firewalls
• Application-level Firewalls
• Stateful Inspection Firewalls
9.2.1 Packet Filtering Firewalls
Packet filtering firewalls restrict access based on the source/destination computer network
address of a packet and the type of application.