Inferring higher level policies from firewall rules

Packet filtering firewall is one of the most important mechanisms used by corporations to enforce their security policy. Recent years have seen a lot of research in the area of firewall management. Typically, firewalls use a large number of low-level filtering rules which are configured using vendor-specific tools. System administrators start off by writing rules which implement the security policy of the organization. They add/delete/change order of rules as the requirements change. For example, when a new machine is added to the network, new rules might be added to the firewall to enable certain services to/from that machine. Making such changes to the low-level rules is complicated by the fact that the effect of a rule is dependent on its priority (usually determined by the position of the rule in the rule set). As the size and complexity of a rule set increases, it becomes difficult to understand the impact of a rule on the rule set. This makes management of rule sets more error prone. This is a very serious problem as errors in firewall configuration mean that the desired security policy is not enforced.