Software-Defined Networking (SDN) introduces granularity, visibility and flexibility to networking, which separates the control-logic from networking devices. SDN programmatically modifies the functionality and behaviour of network devices. It separates control plane and data plane, and thus provides centralized control. Though SDN provides better performance but there are some security issues that need to be taken care of. This includes firewalls, monitoring applications, IDS(Intrusion detection systems) etc. Therefore, this research work reviews the related approaches which have been proposed by identifying their firewall scope, their practicability, their advantages and drawbacks related with SDN. This paper describes the firewall policies as the forth new security challenges. Keywords: Software defined networking, Architecture, OpenFlow, Firewalls, Anomaly detection