For years the government has been using CDS to bridge networks with different classification levels. This talk will focus on what CDS systems are, how they’re built, and what kind of configurations are common in the wild. Furthermore, we’ll look at testing techniques to evaluate the security of these systems and potential ways to exploit holes in configuration and design. We’ll also look at the ways the commercial world might benefit from a data and type-driven firewall as well as some of the downfalls and negative aspects of implementing a cross-domain system.