Firewall Modules and Modular Firewalls
Topics to be covered
What is a Firewall
How does a firewall works
Dependency explained
Order of Rules matters
New Metric …?
Fields, Packets, Rules and Firewalls
Dependency metric
Theorem-2
Inversion Metric – Theorem – 3
Theorem 4
Simple Firewalls
Identifying irrelevant rules
Algorithm for removing Irrelevant rules
Partitioned Firewalls
Theorem 5Modular firewall
Theorem 6
Algorithm2
Theorem 7
Design goal
Simulation Results
Conclusion

Theorem-2

Let ‘F’ be any firewall with ‘n’ rules
The smallest possible value of dependency metric is (n-1)/n.
The largest possible value of dependency metric is (n-1)/2.
Proof :
Consider ‘F’ has only 2 bands , first one has n-1 rules and other has 1 rule. Average cardinality of dependency set (n-1)/n.
Consider ‘F’ has ‘n’ bands and each band consists of only 1 rule,
dep. set of first rule – 0 rules, 2nd rule – 1 rule , nth rule – n-1 rules. Average cardinality (n-1)/2.