Abstract: Denial of Service (DoS) attacks represent a significant danger and one of the most persistent securityconcernsincontemporary Internet infrastructure. DDoS attacks can be profoundly destructive, often occurring with minimal or no advancenotice.ADDoS attack can rapidly incapacitate the processing and communication capacities of its target within a brief timeframe. Theseverityofthe issue has necessitated the adoption of several defence methods to counter these attacks. Integrated systems, includingwebservers,database servers, and cloud computing servers, have been jeopardised by network adversaries. Managing a DDoS attackis trickybecauseit is hard to tell what traffic is legal and what is malicious especially when the traffic is caused by different scatteredsourceswithdifferent rates. As such, distributed denial-of-service (DDoS) attacks are better prevented proactively than addressed reactively. Inthiswork, we present a hierarchical taxonomy of the tools used in the DDoS attack and a taxonomy of defense mechanisms used to alleviate such threats. The main goal is to structure both the attack and defense strategy systematically and to enhance knowledge of the problem and remedy of the DDoS environment. Keywords: DDoS Attack, DDoS Tools, Taxonomy, Threats and Mitigation Techniques, Defense Mechanism