Rule Logic Overview - ZyXEL Communications ZyWall 100 User Manual

ZyWALL 100 Internet Security Gateway

16.2 Rule Logic Overview

16.2.1 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 is the direction of traffic does the rule apply to: 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?
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.
16.2.2 Security Ramifications
Once the logic of the rule has been defined, it is critical to consider the security ramifications created by the
rule:
1. Does this rule stop LAN users from accessing critical resources on the Internet? For example, if IRC is
blocked, are there users that require this service?
2. Is it possible to modify the rule to be more specific? For example, if IRC is blocked for all users, will a
rule that blocks just certain users be more effective?
3. Does a rule that allows Internet users access to resources on the LAN create a security vulnerability? For
example, if FTP ports (TCP 20, 21) are allowed from the Internet to the LAN, Internet users may be able
to connect to computers with running FTP servers.
4. Does this rule conflict with any existing rules?
Once these questions have been answered, adding rules is simply a matter of plugging the information into
the correct fields in the web configurator screens.
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Study these points carefully before configuring rules.
Creating Custom Rules