ZyXEL ADSL Prestige 2602R-61 VoIP 91-006-024004B Manual Do Utilizador

Prestige 2602R Series User’s Guide

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Chapter 13 Firewall Configuration

Note: If you configure firewall rules without a good understanding of how they work, 

you might inadvertently introduce security risks to the firewall and to the 
protected network. Make sure you test your rules after you configure them.

For example, you may create rules to:

• Block certain types of traffic, such as IRC (Internet Relay Chat), from the LAN to the 

Internet.

• Allow certain types of traffic, such as Lotus Notes database synchronization, from 

specific hosts on the Internet to specific hosts on the LAN.

• 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. 

Note: Study these points carefully before configuring rules.

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.”

1 Is the intent of the rule to forward or block traffic?

2 What direction of traffic does the rule apply to (refer to 

)?

3 What IP services will be affected?

4 What computers on the LAN are to be affected (if any)?

5 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?