Traditional software-defined network (SDN) systems focus primarily based on a north–south data flow to enable centralized control of network devices. However, the growing complexity and scale of modern networks, driven by emerging internet applications and services, require a more advanced approach to handle the east–west data flow, which involves communication between devices within the network. This necessitates a distributed SDN architecture with multiple controllers to simplify network management and achieve control. This paper evaluates a modified east–west interface with network policies for Distributed Control Plane Networks, designed to meet the needs of SDN in multi-domain networks such as wide area networks (WANs) while ensuring network availability. The modified east–west interface is developed by implementing network policies on a Modified Communication Interface for Distributed Control Plane (mCIDC), which is integrated with the Floodlight controller. Experimental results demonstrate that the mCIDC outperforms the Communication Interface for Distributed Control Plane (CIDC) by reducing captured transmission control protocol (TCP) packets by 15.51%, TCP errors by 29.85%, and inter-controller communication overload by 22.98%. This indicates that the mCIDC can make better decisions in line with network policies compared to the CIDC when deployed in a real-time wide-area network. This shows that SDN architectures can support network policies for management, security, and interoperability network devices.