Rule Logic Overview - ZyXEL Communications ZyWALL 5 User Manual

ZyWALL 5 Internet Security Appliance
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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.
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.

10.3 Rule Logic Overview

Study these points carefully before configuring rules.
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 (refer to 10.2)?
4. What IP services will be affected?
5. What computers on the LAN or DMZ are to be affected (if any)?
6. What computers on the Internet will be affected? The more specific, the better. For example, if
traffic is being allowed from the Internet to the LAN, it is better to allow only certain machines on
the Internet to access the LAN.
10.3.2 Security Ramifications
Once the logic of the rule has been defined, it is critical to consider the security ramifications created
by the rule:
10-2 Firewall Screens