ZyXEL Communications ZyWALL5UTM 4.0 User Manual

ZyWALL 5/35/70 Series User’s Guide

Chapter 11 Firewall Screens

212

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.