ZyXEL Communications 5 Series - Manual (Page 227)

ZyWALL 5/35/70 Series User’s Guide
Chapter 11 Firewall 227
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.
11.5 Firewall Rules Example
Suppose that your company decides to block all of the LAN users from using IRC (Internet
Relay Chat) through the Internet. To do this, you would configure a LAN to WAN firewall
rule that blocks IRC traffic from any source IP address from going to any destination address.
You do not need to specify a schedule since you need the firewall rule to always be in effect.
The following figure shows the results of this rule.
Figure 112 Blocking All LAN to WAN IRC Traffic Example
Your firewall would have the following configuration.
• The first row blocks LAN access to the IRC service on the WAN.
Table 64 Blocking All LAN to WAN IRC Traffic Example
# SOURCE DESTINATION SCHEDULE SERVICE ACTION
1 Any Any Any IRC Drop
Default Any Any Any Any Allow