ZyWALL 5/35/70 Series User’s Guide
11.3 Rule Logic Overview
Note: Study these points carefully before configuring rules.
11.3.1Rule Checklist
1State 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.
2Is the intent of the rule to forward or block traffic?
3What direction of traffic does the rule apply to (see Section 10.2 on page 198)?
4What IP services will be affected?
5What computers on the LAN or DMZ are to be affected (if any)?
6What 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.
11.3.2Security Ramifications
Once the logic of the rule has been defined, it is critical to consider the security ramifications created by the rule:
1Does 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?
2Is 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?
3Does 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.
4Does 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.
11.3.3 Key Fields For Configuring Rules
11.3.3.1 Action
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
Chapter 11 Firewall Screens | 212 |