Rule Logic Overview; Rule Checklist; Security Ramifications; Key Fields For Configuring Rules - ZyXEL Communications Prestige 662HW Series User Manual

Prestige 662HW Series User's Guide
♦ 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 Prestige's default rules.

12.3 Rule Logic Overview

Study these points carefully before configuring rules.

12.3.1 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 12.2)?
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.

12.3.2 Security Ramifications

Once the logic of the rule has been defined, it is critical to consider the security ramifications created
by the rule:
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.

12.3.3 Key Fields For Configuring Rules

Action
Should the action be to Block or Forward?
12-2 Firewall Configuration