Rule Logic Overview - ZyXEL Communications ZyXEL ZyWALL 2WE User Manual

ZyWALL 2 and ZyWALL 2WE
♦ 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.

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 direction of traffic does the rule apply to (refer to 16.1)?
4. What IP services will be affected?
5. What computers on the LAN 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?
16-2
Study these points carefully before configuring rules.
Creating Custom Rules