Firewall policy verification and troubleshooting

Firewalls are important elements of enterprise security and have been the most widely adopted technology for protecting private networks. The quality of protection provided by a firewall mainly depends on the quality of its policy (i.e., configuration). However, due to the lack of tools for verifying and troubleshooting firewall policies, most firewalls on the Internet have policy errors. A firewall policy can error either create security holes that will allow malicious traffic to sneak into a private network or block legitimate traffic disrupting normal traffic, which in turn could lead to diestrous consequences. We propose a firewall verification and troubleshooting tool in this paper. Our tool takes as input a firewall policy and a given property, then outputs whether the policy satisfies the property. Furthermore, in the case that a firewall policy does not satisfy the property, our tool outputs which rules cause the verification failure. This provides firewall administrators a basis for how to fix the policy errors. Despite of the importance of verifying firewall policies and finding troublesome rules, they have not been explored in previous work. Due to the complex nature of firewall policies, designing algorithms for such a verification and troubleshooting tool is challenging. In this paper, we designed and implemented a verification and troubleshooting algorithm using decision diagrams, and tested it on both real-life firewall policies and synthetic firewall policies of large sizes. The performance of the algorithm is sufficiently high that they can practically be used in the iterative process of firewall policy design, verification, and maintenance. The firewall policy troubleshooting algorithm proposed in this paper is not limited to firewalls. Rather, they can be potentially applied to other rule-based systems as well.