The Internet of Things (IoT) is an arrangement of connected numerous digital devices usually contained Unique Identifiers (UIDs) and have the capability to exchange data over a network without any human interaction. Another new paradigm Software-Defined Networking (SDN) comes in for the organization and control of the large amount of data produced by IoT devices. It separates the data plane from the control plane of network devices which enables easy configuration and management of those devices. Furthermore, Network Function Virtualization (NFV) is emerged to optimize and secure the SDN-IoT network. It enables network devices to be deployed as virtualized components via software. In this research, the authors have proposed an SDN based distributed IoT network with NFV implementation for smart cities. Where smart city is a residential area which utilizes Information and Communication Technology (ICT) as well as IoT network to develop the standard of living of its residents. The integration of NFV in the SDN-IoT network improves the network performance by increasing throughput, and time sequence while mitigating the round trip time as well. Moreover, the authors have used multiple distributed controllers and a clustering scheme to improve load balancing, scalability, availability, integrity, and security of the whole network.