ZyXEL Communications ZyXEL ZyWALL 35 - Manual (Page 188)

ZyWALL 35 User’s Guide
186 Chapter 10 Firewall Screens
• WAN to LAN
• WAN to WAN/ZyWALL
This prevents computers on the WAN from using the ZyWALL as a gateway to
communicate with other computers on the WAN and/or managing the ZyWALL.
• DMZ to LAN
• DMZ to DMZ/ZyWALL
This prevents computers on the DMZ from communicating between networks or subnets
connected to the DMZ interface and/or managing the ZyWALL.
You may define additional rules and sets or modify existing ones but please exercise extreme
caution in doing so.
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.
10.3 Rule Logic Overview
10.3.1 Rule Checklist
1 State the intent of the rule. For example, This restricts all IRC access from the LAN to the
Internet. Or, This allows a remote Lotus Notes server to synchronize over the Internet to
an inside Notes server.
2 Is the intent of the rule to forward or block traffic?
3 What direction of traffic does the rule apply to ( see the Types of Firewalls section )?
Note: 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.
Note: Study these points carefully before configuring rules.