## 9 Conclusions  
The connected vehicles in the IoV are advancing in a highly powerful and complex condition that provides driver choices in basic circumstances. Specifically, VANETs are generally acknowledged as a foundation for enabling the security, privacy, safety, traffic, and infotainment based servicesand applications for drivers, travelers, and people walking on the roads in the IoV. In reality, these profoundly portable systems are relied upon to add to road security and safety by giving the appropriate data to the drivers on the potential threats inside their environment. In any case, a VANET is certainly not a benign domain, inferable from its immense working region and the hidden advancements used to convey basic data. As far as growing the vehicles on the roads, it is difficult to manage the data and the security threats produced by the vehicles and the adversaries by the traditional VANETs, so there is a need for a platform that manages all the difficulties in the traditional VANETS. The best solution is to utilize the SDN in the VANETs.  
The SDN-based VANETs are a system innovation dependent on the partition of information and control and application planes. This paper for the most part centers around examining certain literature that focuses on characterizing existing SDN-based VANETs dependent on their demonstration and execution. We additionally discuss the SDN-based ITS, and SDN-based VANETs in detail. Security is one of the basic concerns in a vehicular system. Throughout the years, various security arrangements has been conceived for VANETs that principally depend on customary cryptographic plans using open key frameworks and endorsements. Eventually, cryptographic based solutions are not attainable for the vehicular systems since the vehicles are profoundly unique in their environment and are disseminated all through the system. The accessibility of a systems administration framework cannot be ensured consistently, and customary cryptography-based arrangements are likewise helpless against insider attacks.  
Subsequently, trust has been as of late presented as an option for guaranteeing security in the vehicular systems. We furthermore examined the security attacks alongside the taxonomy of the security measure in the SDN, and every single imaginable attack with models that would occur in SDN-based VANETs. What is more, this work gives a brief overview of the present investigations available in the literature on applications in support of SDN-based VANETs. The key thoughts of SDN-based VANETs and their administrations and applications were likewise presented. We also discussed the overview of the challenges that are available in the SDN-based VANET literature. In this paper we explain the details of the security attacks in future SDN-based VANETs. Where SDN-based VANETs provide some benefits in terms of applications and services, some SDN-based VANETs have important challenges which need to be solved. In this study we discuss and elaborate the challenges, along with the applications. At the end, we also discussed some guidelines for future research directions.  
M.A., writing, original draft preparation, designing, analysis, editing. O.G., A.B., and P.T., review, editing, investigation. V.E.B., help in methodology investigation, and content verification. G.W., supervision, review, content verification, editing, resources and funding acquisition. J.C., review and editing the content. All the authors also contributed in writing, reviewing, and structured the work. All authors have read and agreed to the published version of the manuscript.  
This work was supported in part by the National Natural Science Foundation of China under Grant 61632009 and Grant 61472451, in part by the Guangdong Provincial Natural Science Foundation under Grant 2017A0308006, and in part by the High-Level Talents Program of Higher Education in Guangdong Province under Grant 2016 ZJ01.  
The authors declare no conflicts of interest.