Abstract
The Distributed Denial of Service (DDoS) attack is one of the most critical issues in network security. These sorts of attacks pose a noteworthy danger to the accessibility of network services for their legitimate users by flooding the bandwidth or network service using various infected computer systems. The targeted servers are overwhelmed with malicious packets or connection requests, causing them to slow down or even crash the server operations which results in preventing genuine users from accessing the service. In this paper, we discussed the detailed classification of DDoS attacks and identified attackers' motivations behind them and their consequences. Further, the DDoS attacks on IoT devices are elaborated based on applications and network layers. A comprehensive literature review has been conducted on cutting-edge defense techniques to defend against such attacks. An in-depth analysis of each mechanism has been carried out to find the optimal solutions. We fairly evaluated the existing defense techniques for DDoS attacks and presented key findings in comparison tables. Furthermore, this paper provides recommendations for future work for new researchers.