ZyXEL 2WG Guida Utente

Chapter 12 Firewall Screens

ZyWALL 2WG User’s Guide

If everything is working properly, you probably do not need to change the threshold settings as 
the default threshold values should work for most small offices. Tune these parameters when 
you believe the ZyWALL has been receiving DoS attacks that are not recorded in the logs or 
the logs show that the ZyWALL is classifying normal traffic as DoS attacks. Factors 
influencing choices for threshold values are:

1 The maximum number of opened sessions.
2 The minimum capacity of server backlog in your LAN network.
3 The CPU power of servers in your LAN network.
4 Network bandwidth. 
5 Type of traffic for certain servers.

Reduce the threshold values if your network is slower than average for any of these factors 
(especially if you have servers that are slow or handle many tasks and are often busy). 
If you often use P2P applications such as file sharing with eMule or eDonkey, it’s 
recommended that you increase the threshold values since lots of sessions will be established 
during a small period of time and the ZyWALL may classify them as DoS attacks.

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Incorrectly configuring the firewall may block valid access or introduce security 
risks to the ZyWALL and your protected network. Use caution when creating or 
deleting firewall rules and test your rules after you configure them.

Consider these security ramifications before creating a 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 entering the 
information into the correct fields in the web configurator screens.