## 2 Background
### Overview of DoS and DDoS Attacks on CC
#### 2.2.1 DoS, DDoS Attacks on CC  
Adversaries launch DDoS attacks by sending a large volume of seemingly normal packets, making them difficult to detect. It is transmitted to the victim machine for embezzling the applications or protocol execution on the victim [18; 19]. DDoS attacks that disrupt users' connectivity by exhausting the network bandwidth and reducing the router's processing capacity fall under the network-layer attack category. On the other hand, the attacks that deny legitimate user access to services by exhausting the VM resources (e.g., \begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Service Models** & **Ownership Level** & **Control Level** & **Example** \\ \hline SaaS & End Clients & Can use the app but cannot control it or the server, storage, operating system (OS), network interface card (NIC), antivirus, etc. & Google and Microsoft applications \\ PaaS & Software Developer & Can create and control own app but cannot control the OS, NIC, antivirus, etc. & GAE, Microsoft’s Azure \\ IaaS & Infrastructure & Can create and control own app, OS, NIC, antivirus, etc. & GoGrid, Flexicale, Layered Technologies, and Rackspace \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of CC service models. \begin{table}
\begin{tabular}{p{42.7 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Deployment Models** & **Ownership** & **Services** \\ \hline Private & Owned by Single Company & Serve Internal Clients \\ Public & Owned by Single Company & Serve General Public \\ Community & Owned by Specific Community & Serve to Specific Community \\ Hybrid & Owned by a private company or/and owner of CSP & Serve to the general public and internal clients \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary of CC deployment models. input/output bandwidth, sockets, central process unit (CPU), disk/database bandwidth, and memory) are application-layer (Level 7) attacks [20]. Application-layer attacks target servers' applications or services by attempting to fully exhaust their resources by creating as many transactions and processes in the shortest time possible. Application-layer attacks are most challenging to detect and overcome because the generated transactions, such as HTTP requests, are indistinguishable from those by legitimate users. DDoS attacks are executed via a remotely controlled network, distributed and well-organized, so that compromised machines called zombies can be utilized for transmitting a huge volume of simultaneous requests to continuously attack the target system. The widespread adoption of CC causes the number of attacks to also skyrocketed. The commonality of the CC structure's features and components makes it more susceptible to attacks, especially DoS and DDoS. Adversaries typically aimed their DoS or DDoS attacks at CSP with many linked devices because its scalability and dependability make the CC accessible anywhere at any time. DDoS attacks typically involve many malicious packets directed to the target to keep it busy. With traditional networks, there are many strategies to defend against DDoS attacks; however, it is more challenging in the CC environment due to unique CC properties making the defense difficult. This study will look into the existing methods for detecting, preventing, and mitigating DDoS attacks in CC environments [21]. Organizations can leverage the CC to obtain on-demand, elastic, and fully managed computer system resources and services. However, any attacks, especially DoS and DDoS, on CC could cause substantial losses for CSPs and users. Successful DDoS attacks have serious consequences, such as poor user experience, service failures, and, in the worst-case scenario, complete shutdown and financial repercussions. DDoS attacks have grown in volume, regularity, and ferocity as the popularity of the internet of things (IoT) and widespread network connectivity have inadvertently fueled their growth [15]. Fast-growing web-based apps are typically developed and deployed within the CC environment.