Security Ramifications; Key Fields For Configuring Rules; Action; Service - ZyXEL Communications ZyWall 35 User Manual

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

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.
Chapter 10 Firewall Screens
Section 10.8 on page 192
ZyWALL 35 User's Guide
for more information on predefined services.
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