Network security management is one of the most topical concerns of information security (IS) in modern enterprises. Due to great variety and increasing complexity of network security systems (NSSs) there is a challenge to manage them in accordance with IS policies. Incorrect configurations of NSSs lead to outages and appearance of vulnerabilities in networks. Moreover, policy management is a time and resource consuming process, which takes significant amount of manual work. The paper discusses issues of policy management process in its application for NSSs and describes a policy model aimed to facilitate the process by means of specification of IS policies independently on platforms of NSSs, selection of the most effective NSSs aligned with the policies, and implementation of the policies in configurations of the NSSs.