Development of Software Defined Networking (SDN) based Vehicular Ad Hoc Networks (VANETs) is one of the key enablers of 5G technology. VANETs enable different types of services through communication between vehicles and road side units. Intelligent Transportation System (ITS) introduced this emerging technology to provide travelers comfort, safety, and infotainment services with improved traffic efficiency. Traditional VANET is not sufficient to handle dynamic and large scale networks with their fixed and embedded policies, and complex architecture. Open Network Foundation (ONF) is promoting the adoption of SDN through open standards' development by facilitating logical and centralized control of the entire network. SDN enables VANET to be a flexible and programmable network with the advent of new services and features. A centralized controller in the control plane controls the overall network functionalities and forwarding of data packets through the forwarding devices in the data plane. SDN enhances the efficiency of VANET and provides security benefits to VANET. But, it causes new security problems also with the integration of new technologies and architectural components in the network. This article provides a comprehensive review of VANET, SDN, and SDN based VANETs based on their architectural and implementation details. Then it explains the effect of SDN on the security of VANET when it is integrated with traditional VANET. This paper encompasses a comprehensive review of proposed approaches providing security solutions for SDN based VANETs and outlines emerging research issues as future directions. To the best of our knowledge, this is the first article presenting the comprehensive review of security aspects of SDN based VANET considering architectural and security services on different layers of a network.

基于软件定义网络（SDN）的车载自组织网络（VANET）的开发是5G技术的关键推动力之一。VANET通过车辆和路边单元之间的通信来启用不同类型的服务。智能交通系统（ITS）引入了这项新兴技术，旨在为旅行者提供舒适，安全和信息娱乐服务，并提高交通效率。传统的VANET不足以处理具有固定和嵌入式策略以及复杂体系结构的动态大型网络。开放网络基金会（ONF）通过促进整个网络的逻辑和集中控制，通过开放标准的开发来促进SDN的采用。随着新服务和功能的出现，SDN使VANET成为灵活的可编程网络。控制平面中的中央控制器控制整个网络功能以及通过数据平面中的转发设备转发数据包。SDN可以提高VANET的效率，并为VANET提供安全优势。但是，随着网络中新技术和体系结构组件的集成，它也会引起新的安全问题。本文根据其架构和实现细节，对VANET，SDN和基于SDN的VANET进行了全面的回顾。然后说明了SDN与传统VANET集成时对SDN的影响。本文包括对为基于SDN的VANET提供安全解决方案的提议方法的全面综述，并概述了新兴的研究问题，并将其作为未来的发展方向。据我们所知，