ZyXEL Communications ZyWALL 10, User Manual

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ZyWALL 10 Internet Security Gateway
16-2 Creating Custom Rules
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 PCs 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 Rules screen in the ZyWALL Web Configurator.
16.2.3 Key Fields For Configuring Rules
Action
Should the action be to Block or Forward ?
Please note that “block” means the firewall silently discards the packet.
Service
Select the service from the Service scrolling list box. If the service is not listed, it is necessary to first define
it. See section 16.4 for more information on services.
Source Address
What is the connection’s source address; is it on the LAN or WAN? Is it a single IP, a range of IPs or a
subnet?
Destination Address
What is the connection’s destination address; is it on the LAN or WAN? Is it a single IP, a range of IPs or a
subnet?