Rule Logic Overview; Rule Checklist; Security Ramifications; Key Fields For Configuring Rules - ZyXEL Communications Internet Security Appliance ZyWALL5UTM 4.0 User Manual

Internet security appliance

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11.3 Rule Logic Overview

Note: Study these points carefully before configuring rules.

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

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.

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.

Should the action be to Drop, Reject or Permit?

Note: "Drop" means the firewall silently discards the packet. "Reject" means the

firewall discards packets and sends an ICMP destination-unreachable

message to the sender.

Chapter 11 Firewall Screens

ZyWALL 5/35/70 Series User's Guide

Section 10.2 on page