Computer network security is the first line of defence to accomplish information assurance. The computer network is at risk without a well-designed and flawless implemented network security policy. The main problem is that network administrators are not able to verify the network security policy. Although further research has been carried out, it mainly concerns small specific parts of the overall problem. This paper presents different approaches from literature and highlights how they are correlated and can operate together. This work summarizes the solutions proposed in literature, points out their advantages, disadvantages and limitations. To conclude, it proposes solutions for future research in this area.