Nortel BSR222, Configuration, Page: 173 / 451

Chapter 11 Firewall screens 173
Nortel Business Secure Router 222 Configuration — Basics
Rule logic overview
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.”
2 Is the intent of the rule to forward or block traffic?
3
What direction of traffic does the rule apply to?
4 What IP services are affected?
5 What computers on the LAN are affected (if any)?
6 What computers on the Internet are affected? The more specific, the better.
For example, if traffic is allowed from the Internet to the LAN, it is better to
allow only certain machines on the Internet to access the LAN.
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, a rule that blocks just certain users can 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 can connect to computers with
running FTP servers.
4
Does this rule conflict with any existing rules?
Note: Study these points carefully before configuring rules.