Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Computer Science


This dissertation describes a technique for formally analyzing a firewall security policy using a quasi-reduced multiway decision diagram model. The analysis allows a system administrator to detect and repair errors in the configuration of the firewall without a tedious manual inspection of the firewall rules.;We present four major contributions. First, we describe a set of algorithms for representing a firewall rule set as a multi-way decision diagram and for solving logical queries against that model. We demonstrate the application of these techniques in a tool for analyzing iptables firewalls. Second, we present an extension of our work that enables analysis of systems of connected firewalls and firewalls that use network address translation and other packet mangling rules. Third, we demonstrate a technique for decomposing a network into classes of equivalent hosts. These classes can be used to detect errors in a firewall policy without apriori knowledge of potential vulnerabilities. They can also be used with other firewall testing techniques to ensure comprehensive coverage of the test space. Fourth, we discuss a strategy for partially automating repair of the firewall policy through the use of counterexamples and rule history.;Using these techniques, a system administrator can detect and repair common firewall errors, such as typos, out-of-order rules, and shadowed rules. She can also develop a specification of the behaviors of the firewall and validate the firewall policy against that specification.



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