ZyXEL Communications ZyXEL ZyWALL 5 - Manual (Page 168)

ZyWALL 5 User’s Guide
Chapter 10 Firewall Screens 167
10.3.2 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 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.
10.3.3 Key Fields For Configuring Rules
10.3.3.1 Action
Should the action be to Block or Forward?
Note: “Block” means the firewall silently discards the packet.
10.3.3.2 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 10.8 on page 180 for more information on predefined services.
10.3.3.3 Source Address
What is the connection’s source address; is it on the LAN, DMZ or WAN? Is it a single IP, a
range of IPs or a subnet?
10.3.3.4 Destination Address
What is the connection’s destination address; is it on the LAN, DMZ or WAN? Is it a single
IP, a range of IPs or a subnet?
10.4 Connection Direction Examples
This section describes examples for firewall rules for connections going from LAN to WAN
and from WAN to LAN. Rules for the DMZ work in a similar fashion.