As IoT-based smart city networks expand rapidly, they face critical challenges regarding security, scalability, and network management. A Blockchain-enabled Software-Defined Networking (SDN) framework integrating a queueing model for increased security and scalability is presented in this study to address these concerns. Decentralized, tamper-resistant data management is provided by blockchain, while dynamic network traffic management is provided by SDN. SDN emulation is provided by Mininet-WiFi, blockchain security is provided by Ethereum, and optimized routing is delivered by OpenFlow. As a result of simulations, data delivery rates were improved, delays were reduced, and cyber threats, specifically DDoS attacks, were made more resilient. IoT infrastructure for smart cities can be made more secure and scalable through the integration of Blockchain and SDN.