Administrator’s Handbook
An approach to using filters
The ultimate goal of network security is to prevent unauthorized access to the network without compromis- ing authorized access. Using filter sets is part of reaching that goal.
Each filter set you design will be based on one of the following approaches:
•That which is not expressly prohibited is permitted.
•That which is not expressly permitted is prohibited.
It is strongly recommended that you take the latter, and safer, approach to all of your filter set designs.
