ZyXEL Communications Internet Security Gateway ZyWALL 100 - Manual (Page 171)

ZyWALL 100 Internet Security Gateway
Creating Custom Rules 16-1
Chapter 16
Creating Custom Rules
This chapter contains instructions for defining both Local Network and Internet rules.
16.1 Rules Overview
Firewall rules are grouped based on the direction of travel of packets to which they apply, whether WAN to
LAN, LAN to WAN, WAN to DMZ, DMZ to WAN, DMZ to LAN, LAN to DMZ, WAN to WAN, LAN to
LAN or DMZ to DMZ. By default, the ZyWALL’s stateful packet inspection allows all communications to
the Internet that originate from the local network, and blocks all traffic to the LAN that originates from the
Internet. It also allows all communications between the DMZ and the Internet or from the LAN to the DMZ,
but blocks all sessions from the DMZ to the LAN. You may define additional rules and sets or modify
existing ones but please exercise extreme caution in doing so.
If you configure firewall rules without a good understanding of how they work, you
might inadvertently introduce security risks to the firewall and to the protected
network. Make sure you test your rules after you configure them.
For example, you may create rules to:
♦ Block certain types of traffic, such as IRC (Internet Relay Chat), from the LAN to the Internet.
♦ Allow certain types of traffic, such as Lotus Notes database synchronization, from specific hosts on the
Internet to specific hosts on the LAN.
♦ Allow everyone except your competitors to access a Web server.
♦ Restrict use of certain protocols, such as Telnet, to authorized users on the LAN.
These custom rules work by comparing the Source IP address, Destination IP address and IP protocol type of
network traffic to rules set by the administrator. Your customized rules take precedence and override the
ZyWALL’s default rules.