The moving target defense (MTD) strategy allows defenders to limit the effectiveness of attacker reconnaissance and exploitation. Many academic works have created MTDs in different deployment environments. However, network-based MTDs (NMTDs) share key components and properties that determine their effectiveness. In this work, we identify and define seven properties common to NMTDs which are key to ensuring the effectiveness of the approach. We then evaluate four NMTD systems using these properties and found two or more key concerns for each of the systems. This analysis shows that these properties may help guide developers of new NMTD systems by guiding the evaluation of these systems and can be used by others as a rubric to assess the strengths and limitations of each NMTD approach.