A good rule of thumb is to have no more then 30 rules. With 30 rules, its relatively easy to understand what is going on. Between 30 and 50 rules, things become confusing, the odds grow exponentially that something will be misconfigured. Anything over 50 rules and you end up fighting a losing battle. When you start having this many rules, you need to take a serious look at your overall security architecture, and not just your firewalls.
Fewer rules have the added bonus of improving performance.
By parsing only a small number of rules, your firewall saves CPU cycles. Most firewalls are extremelly efficient, so you will see little difference. But it can never hurt. Well, we will do just that in this paper. We will go through step by step and build a firewall rulebase.