ZyXEL Communications P-660W-T1 v2, User Manual

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Chapter 11 Firewall Configuration
P-660W-Tx v2 User’s Guide
127
11.7.2.1 Rule Checklist
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?
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.
11.7.2.2 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?
5 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.
11.7.2.3 Key Fields For Configuring Rules
Action
Should the action be to Block or Forward ? “Block” means the firewall silently discards the
packet.
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 11.4.2 on page 121 for more information on predefined services.
Source Address
What is the connection’s source address; is it on the LAN, WAN? Is it a single IP, a range of
IPs or a subnet?
Destination Address
What is the connection’s destination address; is it on the LAN, WAN? Is it a single IP, a range
of IPs or a subnet?