ZyXEL Communications P-661H Series User Manual

P-661H/HW Series User’s Guide

This chapter gives some background information on firewalls and introduces the ZyXEL 
Device firewall.

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 

 to configure default firewall settings. 

 to view firewall rules. 

 to configure firewall rules. 

 to configure a custom service. 

 to configure firewall thresholds. 

There are three main types of firewalls:

• Packet Filtering Firewalls
• Application-level Firewalls
• Stateful Inspection Firewalls

Packet filtering firewalls restrict access based on the source/destination computer network 
address of a packet and the type of application.