Rule Checklist; Security Ramifications - ZyXEL Communications VANTAGE CNM User Manual

Vantage CNM User's Guide
• Block certain types of traffic, such as IRC (Internet Relay Chat), from the LAN to the
Internet.
• Allow certain types of traffic, such as Lotus Notes database synchronization, from
specific hosts on the Internet to specific hosts on the LAN.
• Allow everyone except your competitors to access a Web server.
• Restrict use of certain protocols, such as Telnet, to authorized users on the LAN.

12.4.7 Rule Checklist

1. 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 or DMZ 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.

12.4.8 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.
179 Chapter 12 Configuration > Firewall